[Numpy-discussion] array operation

Dave Bazell bazell at comcast.net
Tue Jan 21 12:33:35 CST 2003


I am trying to see if I can use where() or choose() to do this.  I can't
really figure it out.

I have a 2-d array data where each row is an observation and each column is
an attribute of the observation:

data =
[[.3, .2, 2.3,...]    <- observation 1
 [.7, 1.2, .4...]     <- observation 2
...]]

I have another 1-d array that contains a code for the class of object:

class = [0,1,0,1,1,3,2,0,...]

where class[i] = the class of the ith object in the data array.  Thus,
observation 1 above is class 0, observation 2 is class 1, and so on.

I want to select all objects of a given class from data array.  I can do
this with a loop

for i in range(ndat):
    if class == 0:
        do something
   ....

Is there a way to use where() or choose() to do this?  Would it be more
efficient?

Thanks,

Dave






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