[SciPy-User] re[SciPy-user] moving for loops...

Benjamin Root ben.root@ou....
Tue Jun 8 21:39:11 CDT 2010


Correction for me as well.  To mask out the negative values, use masked
arrays.  So we will turn jules_2d into a masked array (second line), then
all subsequent commands will still work as expected.  It is very similar to
replacing negative values with nans and using nanmin().

> jules_2d = jules.reshape((-1, 12))
> jules_2d = np.ma.masked_array(jules_2d, mask=jules_2d < 0.0)
> jules_monthly = np.mean(jules_2d, axis=0)
> print jules_monthly.shape
  (12,)

Ben Root

On Tue, Jun 8, 2010 at 7:49 PM, Benjamin Root <ben.root@ou.edu> wrote:

> The np.mod in my example caused the data points to stay within [0, 11] in
> order to illustrate that these are months.  In my example, months are
> column, years are rows.  In your desired output, months are rows and years
> are columns.  It makes very little difference which way you have it.
>
> Anyway, let's imagine that we have a time series of data "jules".  We can
> easily reshape this like so:
>
> > jules_2d = jules.reshape((-1, 12))
> > jules_monthly = np.mean(jules_2d, axis=0)
> > print jules_monthly.shape
>   (12,)
>
> voila!  You have 12 values in jules_monthly which are means for that month
> across all years.
>
> protip - if you want yearly averages just change the ax parameter in
> np.mean():
> > jules_yearly = np.mean(jules_2d, axis=1)
>
> I hope that makes my previous explanation clearer.
>
> Ben Root
>
>
> On Tue, Jun 8, 2010 at 5:41 PM, mdekauwe <mdekauwe@gmail.com> wrote:
>
>>
>> OK...
>>
>> but if I do...
>>
>> In [28]: np.mod(np.arange(nummonths*numyears), nummonths).reshape((-1,
>> nummonths))
>> Out[28]:
>> array([[ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>       [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>       [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>       [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>>        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11]])
>>
>> When really I would be after something like this I think?
>>
>> array([  0,  12,  24,  36,  48,  60,  72,  84,  96, 108, 120],
>>        [  1,  13,  25,  37,  49,  61,  73,  85,  97, 109, 121],
>>        [  2,  14,  26,  38,  50,  62,  74,  86,  98, 110, 122]
>>        etc, etc
>>
>> i.e. so for each month jump across the years.
>>
>> Not quite sure of this example...this is what I currently have which does
>> seem to work, though I guess not completely efficiently.
>>
>> for month in xrange(nummonths):
>>         tmp = jules[xrange(0, numyears * nummonths, nummonths),VAR,:,0]
>>        tmp[tmp < 0.0] = np.nan
>>        data[month,:] = np.mean(tmp, axis=0)
>>
>>
>>
>>
>> Benjamin Root-2 wrote:
>> >
>> > If you want an average for each month from your timeseries, then the
>> > sneaky
>> > way would be to reshape your array so that the time dimension is split
>> > into
>> > two (month, year) dimensions.
>> >
>> > For a 1-D array, this would be:
>> >
>> >> dataarray = numpy.mod(numpy.arange(36), 12)
>> >> print dataarray
>> > array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11,  0,  1,  2,  3,
>>  4,
>> >         5,  6,  7,  8,  9, 10, 11,  0,  1,  2,  3,  4,  5,  6,  7,  8,
>>  9,
>> >        10, 11])
>> >> datamatrix = dataarray.reshape((-1, 12))
>> >> print datamatrix
>> > array([[ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>> >        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11],
>> >        [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11]])
>> >
>> > Hope that helps.
>> >
>> > Ben Root
>> >
>> >
>> > On Fri, May 28, 2010 at 3:28 PM, mdekauwe <mdekauwe@gmail.com> wrote:
>> >
>> >>
>> >> OK so I just need to have a quick loop across the 12 months then, that
>> is
>> >> fine, just thought there might have been a sneaky way!
>> >>
>> >> Really appreciated, getting there slowly!
>> >>
>> >>
>> >>
>> >> josef.pktd wrote:
>> >> >
>> >> > On Fri, May 28, 2010 at 4:14 PM, mdekauwe <mdekauwe@gmail.com>
>> wrote:
>> >> >>
>> >> >> ok - something like this then...but how would i get the index for
>> the
>> >> >> month
>> >> >> for the data array (where month is 0, 1, 2, 4 ... 11)?
>> >> >>
>> >> >> data[month,:] = array[xrange(0, numyears * nummonths,
>> >> nummonths),VAR,:,0]
>> >> >
>> >> > you would still need to start at the right month
>> >> > data[month,:] = array[xrange(month, numyears * nummonths,
>> >> > nummonths),VAR,:,0]
>> >> > or
>> >> > data[month,:] = array[month: numyears * nummonths :
>> nummonths),VAR,:,0]
>> >> >
>> >> > an alternative would be a reshape with an extra month dimension and
>> >> > then sum only once over the year axis. this might be faster but
>> >> > trickier to get the correct reshape .
>> >> >
>> >> > Josef
>> >> >
>> >> >>
>> >> >> and would that be quicker than making an array months...
>> >> >>
>> >> >> months = np.arange(numyears * nummonths)
>> >> >>
>> >> >> and you that instead like you suggested x[start:end:12,:]?
>> >> >>
>> >> >> Many thanks again...
>> >> >>
>> >> >>
>> >> >> josef.pktd wrote:
>> >> >>>
>> >> >>> On Fri, May 28, 2010 at 3:53 PM, mdekauwe <mdekauwe@gmail.com>
>> wrote:
>> >> >>>>
>> >> >>>> Ok thanks...I'll take a look.
>> >> >>>>
>> >> >>>> Back to my loops issue. What if instead this time I wanted to take
>> >> an
>> >> >>>> average so every march in 11 years, is there a quicker way to go
>> >> about
>> >> >>>> doing
>> >> >>>> that than my current method?
>> >> >>>>
>> >> >>>> nummonths = 12
>> >> >>>> numyears = 11
>> >> >>>>
>> >> >>>> for month in xrange(nummonths):
>> >> >>>>    for i in xrange(numpts):
>> >> >>>>        for ym in xrange(month, numyears * nummonths, nummonths):
>> >> >>>>            data[month, i] += array[ym, VAR, land_pts_index[i], 0]
>> >> >>>
>> >> >>>
>> >> >>> x[start:end:12,:] gives you every 12th row of an array x
>> >> >>>
>> >> >>> something like this should work to get rid of the inner loop, or
>> you
>> >> >>> could directly put
>> >> >>> range(month, numyears * nummonths, nummonths) into the array
>> instead
>> >> >>> of ym and sum()
>> >> >>>
>> >> >>> Josef
>> >> >>>
>> >> >>>
>> >> >>>>
>> >> >>>> so for each point in the array for a given month i am jumping
>> >> through
>> >> >>>> and
>> >> >>>> getting the next years month and so on, summing it.
>> >> >>>>
>> >> >>>> Thanks...
>> >> >>>>
>> >> >>>>
>> >> >>>> josef.pktd wrote:
>> >> >>>>>
>> >> >>>>> On Wed, May 26, 2010 at 5:03 PM, mdekauwe <mdekauwe@gmail.com>
>> >> wrote:
>> >> >>>>>>
>> >> >>>>>> Could you possibly if you have time explain further your comment
>> >> re
>> >> >>>>>> the
>> >> >>>>>> p-values, your suggesting I am misusing them?
>> >> >>>>>
>> >> >>>>> Depends on your use and interpretation
>> >> >>>>>
>> >> >>>>> test statistics, p-values are random variables, if you look at
>> >> several
>> >> >>>>> tests at the same time, some p-values will be large just by
>> chance.
>> >> >>>>> If, for example you just look at the largest test statistic, then
>> >> the
>> >> >>>>> distribution for the max of several test statistics is not the
>> same
>> >> as
>> >> >>>>> the distribution for a single test statistic
>> >> >>>>>
>> >> >>>>> http://en.wikipedia.org/wiki/Multiple_comparisons
>> >> >>>>> http://www.itl.nist.gov/div898/handbook/prc/section4/prc47.htm
>> >> >>>>>
>> >> >>>>> we also just had a related discussion for ANOVA post-hoc tests on
>> >> the
>> >> >>>>> pystatsmodels group.
>> >> >>>>>
>> >> >>>>> Josef
>> >> >>>>>>
>> >> >>>>>> Thanks.
>> >> >>>>>>
>> >> >>>>>>
>> >> >>>>>> josef.pktd wrote:
>> >> >>>>>>>
>> >> >>>>>>> On Sat, May 22, 2010 at 6:21 AM, mdekauwe <mdekauwe@gmail.com>
>> >> >>>>>>> wrote:
>> >> >>>>>>>>
>> >> >>>>>>>> Sounds like I am stuck with the loop as I need to do the
>> >> comparison
>> >> >>>>>>>> for
>> >> >>>>>>>> each
>> >> >>>>>>>> pixel of the world and then I have a basemap function call
>> which
>> >> I
>> >> >>>>>>>> guess
>> >> >>>>>>>> slows it down further...hmm
>> >> >>>>>>>
>> >> >>>>>>> I don't see much that could be done differently, after a brief
>> >> look.
>> >> >>>>>>>
>> >> >>>>>>> stats.pearsonr could be replaced by an array version using
>> >> directly
>> >> >>>>>>> the formula for correlation even with nans. wilcoxon looks
>> slow,
>> >> and
>> >> >>>>>>> I
>> >> >>>>>>> never tried or seen a faster version.
>> >> >>>>>>>
>> >> >>>>>>> just a reminder, the p-values are for a single test, when you
>> >> have
>> >> >>>>>>> many of them, then they don't have the right size/confidence
>> >> level
>> >> >>>>>>> for
>> >> >>>>>>> an overall or joint test. (some packages report a Bonferroni
>> >> >>>>>>> correction in this case)
>> >> >>>>>>>
>> >> >>>>>>> Josef
>> >> >>>>>>>
>> >> >>>>>>>
>> >> >>>>>>>>
>> >> >>>>>>>> i.e.
>> >> >>>>>>>>
>> >> >>>>>>>> def compareSnowData(jules_var):
>> >> >>>>>>>>    # Extract the 11 years of snow data and return
>> >> >>>>>>>>    outrows = 180
>> >> >>>>>>>>    outcols = 360
>> >> >>>>>>>>    numyears = 11
>> >> >>>>>>>>    nummonths = 12
>> >> >>>>>>>>
>> >> >>>>>>>>    # Read various files
>> >> >>>>>>>>    fname="world_valid_jules_pts.ascii"
>> >> >>>>>>>>    (numpts, land_pts_index, latitude, longitude, rows, cols) =
>> >> >>>>>>>> jo.read_land_points_ascii(fname, 1.0)
>> >> >>>>>>>>
>> >> >>>>>>>>    fname = "globalSnowRun_1985_96.GSWP2.nsmax0.mon.gra"
>> >> >>>>>>>>    jules_data1 = jo.readJulesOutBinary(fname, numrows=15238,
>> >> >>>>>>>> numcols=1,
>> >> >>>>>>>> \
>> >> >>>>>>>>                       timesteps=132, numvars=26)
>> >> >>>>>>>>    fname = "globalSnowRun_1985_96.GSWP2.nsmax3.mon.gra"
>> >> >>>>>>>>    jules_data2 = jo.readJulesOutBinary(fname, numrows=15238,
>> >> >>>>>>>> numcols=1,
>> >> >>>>>>>> \
>> >> >>>>>>>>                       timesteps=132, numvars=26)
>> >> >>>>>>>>
>> >> >>>>>>>>    # grab some space
>> >> >>>>>>>>    data1_snow = np.zeros((nummonths * numyears, numpts),
>> >> >>>>>>>> dtype=np.float32)
>> >> >>>>>>>>    data2_snow = np.zeros((nummonths * numyears, numpts),
>> >> >>>>>>>> dtype=np.float32)
>> >> >>>>>>>>    pearsonsr_snow = np.ones((outrows, outcols),
>> >> dtype=np.float32)
>> >> *
>> >> >>>>>>>> np.nan
>> >> >>>>>>>>    wilcoxStats_snow = np.ones((outrows, outcols),
>> >> dtype=np.float32)
>> >> >>>>>>>> *
>> >> >>>>>>>> np.nan
>> >> >>>>>>>>
>> >> >>>>>>>>    # extract the data
>> >> >>>>>>>>    data1_snow = jules_data1[:,jules_var,:,0]
>> >> >>>>>>>>    data2_snow = jules_data2[:,jules_var,:,0]
>> >> >>>>>>>>    data1_snow = np.where(data1_snow < 0.0, np.nan, data1_snow)
>> >> >>>>>>>>    data2_snow = np.where(data2_snow < 0.0, np.nan, data2_snow)
>> >> >>>>>>>>    #for month in xrange(numyears * nummonths):
>> >> >>>>>>>>    #    for i in xrange(numpts):
>> >> >>>>>>>>    #        data1 =
>> >> >>>>>>>> jules_data1[month,jules_var,land_pts_index[i],0]
>> >> >>>>>>>>    #        data2 =
>> >> >>>>>>>> jules_data2[month,jules_var,land_pts_index[i],0]
>> >> >>>>>>>>    #        if data1 >= 0.0:
>> >> >>>>>>>>    #            data1_snow[month,i] = data1
>> >> >>>>>>>>    #        else:
>> >> >>>>>>>>    #            data1_snow[month,i] = np.nan
>> >> >>>>>>>>    #        if data2 > 0.0:
>> >> >>>>>>>>    #            data2_snow[month,i] = data2
>> >> >>>>>>>>    #        else:
>> >> >>>>>>>>    #            data2_snow[month,i] = np.nan
>> >> >>>>>>>>
>> >> >>>>>>>>    # exclude any months from *both* arrays where we have dodgy
>> >> >>>>>>>> data,
>> >> >>>>>>>> else
>> >> >>>>>>>> we
>> >> >>>>>>>>    # can't do the correlations correctly!!
>> >> >>>>>>>>    data1_snow = np.where(np.isnan(data2_snow), np.nan,
>> >> data1_snow)
>> >> >>>>>>>>    data2_snow = np.where(np.isnan(data1_snow), np.nan,
>> >> data1_snow)
>> >> >>>>>>>>
>> >> >>>>>>>>    # put data on a regular grid...
>> >> >>>>>>>>    print 'regridding landpts...'
>> >> >>>>>>>>    for i in xrange(numpts):
>> >> >>>>>>>>        # exclude the NaN, note masking them doesn't work in
>> the
>> >> >>>>>>>> stats
>> >> >>>>>>>> func
>> >> >>>>>>>>        x = data1_snow[:,i]
>> >> >>>>>>>>        x = x[np.isfinite(x)]
>> >> >>>>>>>>        y = data2_snow[:,i]
>> >> >>>>>>>>        y = y[np.isfinite(y)]
>> >> >>>>>>>>
>> >> >>>>>>>>        # r^2
>> >> >>>>>>>>        # exclude v.small arrays, i.e. we need just less over 4
>> >> >>>>>>>> years
>> >> >>>>>>>> of
>> >> >>>>>>>> data
>> >> >>>>>>>>        if len(x) and len(y) > 50:
>> >> >>>>>>>>            pearsonsr_snow[((180-1)-(rows[i]-1)),cols[i]-1] =
>> >> >>>>>>>> (stats.pearsonr(x, y)[0])**2
>> >> >>>>>>>>
>> >> >>>>>>>>        # wilcox signed rank test
>> >> >>>>>>>>        # make sure we have enough samples to do the test
>> >> >>>>>>>>        d = x - y
>> >> >>>>>>>>        d = np.compress(np.not_equal(d,0), d ,axis=-1) # Keep
>> all
>> >> >>>>>>>> non-zero
>> >> >>>>>>>> differences
>> >> >>>>>>>>        count = len(d)
>> >> >>>>>>>>        if count > 10:
>> >> >>>>>>>>            z, pval = stats.wilcoxon(x, y)
>> >> >>>>>>>>            # only map out sign different data
>> >> >>>>>>>>            if pval < 0.05:
>> >> >>>>>>>>
>>  wilcoxStats_snow[((180-1)-(rows[i]-1)),cols[i]-1]
>> >> =
>> >> >>>>>>>> np.mean(x - y)
>> >> >>>>>>>>
>> >> >>>>>>>>    return (pearsonsr_snow, wilcoxStats_snow)
>> >> >>>>>>>>
>> >> >>>>>>>>
>> >> >>>>>>>> josef.pktd wrote:
>> >> >>>>>>>>>
>> >> >>>>>>>>> On Fri, May 21, 2010 at 10:14 PM, mdekauwe <
>> mdekauwe@gmail.com>
>> >> >>>>>>>>> wrote:
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> Also I then need to remap the 2D array I make onto another
>> >> grid
>> >> >>>>>>>>>> (the
>> >> >>>>>>>>>> world in
>> >> >>>>>>>>>> this case). Which again I had am doing with a loop (note
>> >> numpts
>> >> >>>>>>>>>> is
>> >> >>>>>>>>>> a
>> >> >>>>>>>>>> lot
>> >> >>>>>>>>>> bigger than my example above).
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> wilcoxStats_snow = np.ones((outrows, outcols),
>> >> dtype=np.float32)
>> >> >>>>>>>>>> *
>> >> >>>>>>>>>> np.nan
>> >> >>>>>>>>>> for i in xrange(numpts):
>> >> >>>>>>>>>>        # exclude the NaN, note masking them doesn't work in
>> >> the
>> >> >>>>>>>>>> stats
>> >> >>>>>>>>>> func
>> >> >>>>>>>>>>        x = data1_snow[:,i]
>> >> >>>>>>>>>>        x = x[np.isfinite(x)]
>> >> >>>>>>>>>>        y = data2_snow[:,i]
>> >> >>>>>>>>>>        y = y[np.isfinite(y)]
>> >> >>>>>>>>>>
>> >> >>>>>>>>>>        # wilcox signed rank test
>> >> >>>>>>>>>>        # make sure we have enough samples to do the test
>> >> >>>>>>>>>>        d = x - y
>> >> >>>>>>>>>>        d = np.compress(np.not_equal(d,0), d ,axis=-1) # Keep
>> >> all
>> >> >>>>>>>>>> non-zero
>> >> >>>>>>>>>> differences
>> >> >>>>>>>>>>        count = len(d)
>> >> >>>>>>>>>>        if count > 10:
>> >> >>>>>>>>>>            z, pval = stats.wilcoxon(x, y)
>> >> >>>>>>>>>>            # only map out sign different data
>> >> >>>>>>>>>>            if pval < 0.05:
>> >> >>>>>>>>>>
>> >> wilcoxStats_snow[((180-1)-(rows[i]-1)),cols[i]-1]
>> >> >>>>>>>>>> =
>> >> >>>>>>>>>> np.mean(x - y)
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> Now I think I can push the data in one move into the
>> >> >>>>>>>>>> wilcoxStats_snow
>> >> >>>>>>>>>> array
>> >> >>>>>>>>>> by removing the index,
>> >> >>>>>>>>>> but I can't see how I will get the individual x and y pts
>> for
>> >> >>>>>>>>>> each
>> >> >>>>>>>>>> array
>> >> >>>>>>>>>> member correctly without the loop, this was my attempt which
>> >> of
>> >> >>>>>>>>>> course
>> >> >>>>>>>>>> doesn't work!
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> x = data1_snow[:,:]
>> >> >>>>>>>>>> x = x[np.isfinite(x)]
>> >> >>>>>>>>>> y = data2_snow[:,:]
>> >> >>>>>>>>>> y = y[np.isfinite(y)]
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> # r^2
>> >> >>>>>>>>>> # exclude v.small arrays, i.e. we need just less over 4
>> years
>> >> of
>> >> >>>>>>>>>> data
>> >> >>>>>>>>>> if len(x) and len(y) > 50:
>> >> >>>>>>>>>>    pearsonsr_snow[((180-1)-(rows-1)),cols-1] =
>> >> (stats.pearsonr(x,
>> >> >>>>>>>>>> y)[0])**2
>> >> >>>>>>>>>
>> >> >>>>>>>>>
>> >> >>>>>>>>> If you want to do pairwise comparisons with stats.wilcoxon,
>> >> then
>> >> >>>>>>>>> you
>> >> >>>>>>>>> might be stuck with the loop, since wilcoxon takes only two
>> 1d
>> >> >>>>>>>>> arrays
>> >> >>>>>>>>> at a time (if I read the help correctly).
>> >> >>>>>>>>>
>> >> >>>>>>>>> Also the presence of nans might force the use a loop.
>> >> stats.mstats
>> >> >>>>>>>>> has
>> >> >>>>>>>>> masked array versions, but I didn't see wilcoxon in the list.
>> >> >>>>>>>>> (Even
>> >> >>>>>>>>> when vectorized operations would work with regular arrays,
>> nan
>> >> or
>> >> >>>>>>>>> masked array versions still have to loop in many cases.)
>> >> >>>>>>>>>
>> >> >>>>>>>>> If you have many columns with count <= 10, so that wilcoxon
>> is
>> >> not
>> >> >>>>>>>>> calculated then it might be worth to use only array
>> operations
>> >> up
>> >> >>>>>>>>> to
>> >> >>>>>>>>> that point. If wilcoxon is calculated most of the time, then
>> >> it's
>> >> >>>>>>>>> not
>> >> >>>>>>>>> worth thinking too hard about this.
>> >> >>>>>>>>>
>> >> >>>>>>>>> Josef
>> >> >>>>>>>>>
>> >> >>>>>>>>>
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> thanks.
>> >> >>>>>>>>>>
>> >> >>>>>>>>>>
>> >> >>>>>>>>>>
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> mdekauwe wrote:
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>> Yes as Zachary said index is only 0 to 15237, so both
>> methods
>> >> >>>>>>>>>>> work.
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>> I don't quite get what you mean about slicing with axis >
>> 3.
>> >> Is
>> >> >>>>>>>>>>> there
>> >> >>>>>>>>>>> a
>> >> >>>>>>>>>>> link you can recommend I should read? Does that mean given
>> I
>> >> >>>>>>>>>>> have
>> >> >>>>>>>>>>> 4dims
>> >> >>>>>>>>>>> that Josef's suggestion would be more advised in this case?
>> >> >>>>>>>>>
>> >> >>>>>>>>> There were several discussions on the mailing lists (fancy
>> >> slicing
>> >> >>>>>>>>> and
>> >> >>>>>>>>> indexing). Your case is safe, but if you run in future into
>> >> funny
>> >> >>>>>>>>> shapes, you can look up the details.
>> >> >>>>>>>>> when in doubt, I use np.arange(...)
>> >> >>>>>>>>>
>> >> >>>>>>>>> Josef
>> >> >>>>>>>>>
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>> Thanks.
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>> josef.pktd wrote:
>> >> >>>>>>>>>>>>
>> >> >>>>>>>>>>>> On Fri, May 21, 2010 at 10:55 AM, mdekauwe <
>> >> mdekauwe@gmail.com>
>> >> >>>>>>>>>>>> wrote:
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> Thanks that works...
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> So the way to do it is with np.arange(tsteps)[:,None],
>> that
>> >> >>>>>>>>>>>>> was
>> >> >>>>>>>>>>>>> the
>> >> >>>>>>>>>>>>> step
>> >> >>>>>>>>>>>>> I
>> >> >>>>>>>>>>>>> was struggling with, so this forms a 2D array which
>> >> replaces
>> >> >>>>>>>>>>>>> the
>> >> >>>>>>>>>>>>> the
>> >> >>>>>>>>>>>>> two
>> >> >>>>>>>>>>>>> for
>> >> >>>>>>>>>>>>> loops? Do I have that right?
>> >> >>>>>>>>>>>>
>> >> >>>>>>>>>>>> Yes, but as Zachary showed, if you need the full index in
>> a
>> >> >>>>>>>>>>>> dimension,
>> >> >>>>>>>>>>>> then you can use slicing. It might be faster.
>> >> >>>>>>>>>>>> And a warning, mixing slices and index arrays with 3 or
>> more
>> >> >>>>>>>>>>>> dimensions can have some surprise switching of axes.
>> >> >>>>>>>>>>>>
>> >> >>>>>>>>>>>> Josef
>> >> >>>>>>>>>>>>
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> A lot quicker...!
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> Martin
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> josef.pktd wrote:
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>> On Fri, May 21, 2010 at 8:59 AM, mdekauwe
>> >> >>>>>>>>>>>>>> <mdekauwe@gmail.com>
>> >> >>>>>>>>>>>>>> wrote:
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> Hi,
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> I am trying to extract data from a 4D array and store
>> it
>> >> in
>> >> >>>>>>>>>>>>>>> a
>> >> >>>>>>>>>>>>>>> 2D
>> >> >>>>>>>>>>>>>>> array,
>> >> >>>>>>>>>>>>>>> but
>> >> >>>>>>>>>>>>>>> avoid my current usage of the for loops for speed, as
>> in
>> >> >>>>>>>>>>>>>>> reality
>> >> >>>>>>>>>>>>>>> the
>> >> >>>>>>>>>>>>>>> arrays
>> >> >>>>>>>>>>>>>>> sizes are quite big. Could someone also try and explain
>> >> the
>> >> >>>>>>>>>>>>>>> solution
>> >> >>>>>>>>>>>>>>> as
>> >> >>>>>>>>>>>>>>> well
>> >> >>>>>>>>>>>>>>> if they have a spare moment as I am still finding it
>> >> quite
>> >> >>>>>>>>>>>>>>> difficult
>> >> >>>>>>>>>>>>>>> to
>> >> >>>>>>>>>>>>>>> get
>> >> >>>>>>>>>>>>>>> over the habit of using loops (C convert for my sins).
>> I
>> >> get
>> >> >>>>>>>>>>>>>>> that
>> >> >>>>>>>>>>>>>>> one
>> >> >>>>>>>>>>>>>>> could
>> >> >>>>>>>>>>>>>>> precompute the indices's i and j i.e.
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> i = np.arange(tsteps)
>> >> >>>>>>>>>>>>>>> j = np.arange(numpts)
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> but just can't get my head round how i then use them...
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> Thanks,
>> >> >>>>>>>>>>>>>>> Martin
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> import numpy as np
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> numpts=10
>> >> >>>>>>>>>>>>>>> tsteps = 12
>> >> >>>>>>>>>>>>>>> vari = 22
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> data = np.random.random((tsteps, vari, numpts, 1))
>> >> >>>>>>>>>>>>>>> new_data = np.zeros((tsteps, numpts), dtype=np.float32)
>> >> >>>>>>>>>>>>>>> index = np.arange(numpts)
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> for i in xrange(tsteps):
>> >> >>>>>>>>>>>>>>>    for j in xrange(numpts):
>> >> >>>>>>>>>>>>>>>        new_data[i,j] = data[i,5,index[j],0]
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>> The index arrays need to be broadcastable against each
>> >> other.
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>> I think this should do it
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>> new_data = data[np.arange(tsteps)[:,None], 5,
>> >> >>>>>>>>>>>>>> np.arange(numpts),
>> >> >>>>>>>>>>>>>> 0]
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>> Josef
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> --
>> >> >>>>>>>>>>>>>>> View this message in context:
>> >> >>>>>>>>>>>>>>>
>> >> http://old.nabble.com/removing-for-loops...-tp28633477p28633477.html
>> >> >>>>>>>>>>>>>>> Sent from the Scipy-User mailing list archive at
>> >> Nabble.com.
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>> _______________________________________________
>> >> >>>>>>>>>>>>>>> SciPy-User mailing list
>> >> >>>>>>>>>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>>>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>> _______________________________________________
>> >> >>>>>>>>>>>>>> SciPy-User mailing list
>> >> >>>>>>>>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>>
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> --
>> >> >>>>>>>>>>>>> View this message in context:
>> >> >>>>>>>>>>>>>
>> >> http://old.nabble.com/removing-for-loops...-tp28633477p28634924.html
>> >> >>>>>>>>>>>>> Sent from the Scipy-User mailing list archive at
>> >> Nabble.com.
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>>> _______________________________________________
>> >> >>>>>>>>>>>>> SciPy-User mailing list
>> >> >>>>>>>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>>>>>>
>> >> >>>>>>>>>>>> _______________________________________________
>> >> >>>>>>>>>>>> SciPy-User mailing list
>> >> >>>>>>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>>>>>
>> >> >>>>>>>>>>>>
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>>
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> --
>> >> >>>>>>>>>> View this message in context:
>> >> >>>>>>>>>>
>> >> http://old.nabble.com/removing-for-loops...-tp28633477p28640656.html
>> >> >>>>>>>>>> Sent from the Scipy-User mailing list archive at Nabble.com.
>> >> >>>>>>>>>>
>> >> >>>>>>>>>> _______________________________________________
>> >> >>>>>>>>>> SciPy-User mailing list
>> >> >>>>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>>>
>> >> >>>>>>>>> _______________________________________________
>> >> >>>>>>>>> SciPy-User mailing list
>> >> >>>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>>
>> >> >>>>>>>>>
>> >> >>>>>>>>
>> >> >>>>>>>> --
>> >> >>>>>>>> View this message in context:
>> >> >>>>>>>>
>> >> http://old.nabble.com/removing-for-loops...-tp28633477p28642434.html
>> >> >>>>>>>> Sent from the Scipy-User mailing list archive at Nabble.com.
>> >> >>>>>>>>
>> >> >>>>>>>> _______________________________________________
>> >> >>>>>>>> SciPy-User mailing list
>> >> >>>>>>>> SciPy-User@scipy.org
>> >> >>>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>>
>> >> >>>>>>> _______________________________________________
>> >> >>>>>>> SciPy-User mailing list
>> >> >>>>>>> SciPy-User@scipy.org
>> >> >>>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>>
>> >> >>>>>>>
>> >> >>>>>>
>> >> >>>>>> --
>> >> >>>>>> View this message in context:
>> >> >>>>>>
>> >> http://old.nabble.com/removing-for-loops...-tp28633477p28686356.html
>> >> >>>>>> Sent from the Scipy-User mailing list archive at Nabble.com.
>> >> >>>>>>
>> >> >>>>>> _______________________________________________
>> >> >>>>>> SciPy-User mailing list
>> >> >>>>>> SciPy-User@scipy.org
>> >> >>>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>>
>> >> >>>>> _______________________________________________
>> >> >>>>> SciPy-User mailing list
>> >> >>>>> SciPy-User@scipy.org
>> >> >>>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>>
>> >> >>>>>
>> >> >>>>
>> >> >>>> --
>> >> >>>> View this message in context:
>> >> >>>>
>> http://old.nabble.com/removing-for-loops...-tp28633477p28711249.html
>> >> >>>> Sent from the Scipy-User mailing list archive at Nabble.com.
>> >> >>>>
>> >> >>>> _______________________________________________
>> >> >>>> SciPy-User mailing list
>> >> >>>> SciPy-User@scipy.org
>> >> >>>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>>
>> >> >>> _______________________________________________
>> >> >>> SciPy-User mailing list
>> >> >>> SciPy-User@scipy.org
>> >> >>> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>>
>> >> >>>
>> >> >>
>> >> >> --
>> >> >> View this message in context:
>> >> >>
>> http://old.nabble.com/removing-for-loops...-tp28633477p28711444.html
>> >> >> Sent from the Scipy-User mailing list archive at Nabble.com.
>> >> >>
>> >> >> _______________________________________________
>> >> >> SciPy-User mailing list
>> >> >> SciPy-User@scipy.org
>> >> >> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >>
>> >> > _______________________________________________
>> >> > SciPy-User mailing list
>> >> > SciPy-User@scipy.org
>> >> > http://mail.scipy.org/mailman/listinfo/scipy-user
>> >> >
>> >> >
>> >>
>> >> --
>> >> View this message in context:
>> >> http://old.nabble.com/removing-for-loops...-tp28633477p28711581.html
>> >> Sent from the Scipy-User mailing list archive at Nabble.com.
>> >>
>> >> _______________________________________________
>> >> SciPy-User mailing list
>> >> SciPy-User@scipy.org
>> >> http://mail.scipy.org/mailman/listinfo/scipy-user
>> >>
>> >
>> > _______________________________________________
>> > SciPy-User mailing list
>> > SciPy-User@scipy.org
>> > http://mail.scipy.org/mailman/listinfo/scipy-user
>> >
>> >
>>
>> --
>> View this message in context:
>> http://old.nabble.com/removing-for-loops...-tp28633477p28824023.html
>> Sent from the Scipy-User mailing list archive at Nabble.com.
>>
>> _______________________________________________
>> SciPy-User mailing list
>> SciPy-User@scipy.org
>> http://mail.scipy.org/mailman/listinfo/scipy-user
>>
>
>
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