[Numpy-discussion] Deleting a row from a matrix

Sebastian Haase haase at msg.ucsf.edu
Fri Aug 25 18:24:47 CDT 2006


On Friday 25 August 2006 16:16, Travis Oliphant wrote:
> Sebastian Haase wrote:
> > On Friday 25 August 2006 08:01, Travis Oliphant wrote:
> >> Travis Oliphant wrote:
> >>>> Now of course: I often needed to "insert"  a column, row or section,
> >>>> ... ? I made a quick and dirty implementation for that myself:
> >>>> def insert(arr, i, entry, axis=0):
> >>>>     """returns new array with new element inserted at index i along
> >>>> axis if arr.ndim>1 and if entry is scalar it gets filled in (ref.
> >>>> broadcasting)
> >>>>
> >>>>     note: (original) arr does not get affected
> >>>>     """
> >>>>     if i > arr.shape[axis]:
> >>>>         raise IndexError, "index i larger than arr size"
> >>>>     shape = list(arr.shape)
> >>>>     shape[axis] += 1
> >>>>     a= N.empty(dtype=arr.dtype, shape=shape)
> >>>>     aa=N.transpose(a, [axis]+range(axis)+range(axis+1,a.ndim))
> >>>>     aarr=N.transpose(arr, [axis]+range(axis)+range(axis+1,arr.ndim))
> >>>>     aa[:i] = aarr[:i]
> >>>>     aa[i+1:] = aarr[i:]
> >>>>     aa[i] = entry
> >>>>     return a
> >>>
> >>> Sure, it makes sense to parallel the delete function.
> >>
> >> Although there is already and insert function present in numpy....
> >>
> >> -Travis
> >
> > Yeah - I saw that ...
> > maybe one could introduce consistent namings like
> > arr.copy_insert()
> > arr.copy_delete()
> > arr.copy_append()
>
> I've come up with adding the functions (not methods at this point)
>
> deletefrom
> insertinto
>
> appendto  (syntatic sugar for concatenate but with a separate argument
> for the array and the extra stuff) --- is this needed?

not for me.

-S.




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