Subarray with with arbitrary index?
Hi,
Is it possible to assign to a subarray with arbitrary index?
Suppose I have three arrays
a = arange(8) b = array([2, 3, 5]) c = arange(3)+100
I want a function f, such that calling f(a, b, c) would change a to
[0 1 100 101 4 102 6 7]
This would be useful in certain applications that would otherwise require sparse matrices.
Huaiyu Zhu
On Thu, 16 Aug 2001, Huaiyu Zhu wrote:
Hi,
Is it possible to assign to a subarray with arbitrary index?
Suppose I have three arrays
a = arange(8) b = array([2, 3, 5]) c = arange(3)+100
I want a function f, such that calling f(a, b, c) would change a to
[0 1 100 101 4 102 6 7]
f = Numeric.put f(a, b, c)
put used to be in Python, but it's been in C since some release 17.x.x, I think.
I have a sinking feeling that I must have missed something (no interpreter here to check it works)...
BTW, a week ago I noticed that I had reinvented the wheel in rewriting, in an uglier and less efficient form, Numeric.allclose (hope I got the name right). As far as I can see, it isn't listed in the manual. Did I miss it? All it would need is the docstring copying over.
John
John is right:
a=Numeric.arange(8) b=Numeric.array([2,3,5]) c=Numeric.arange(3)+100 Numeric.put(a,b,c) print a
[ 0 1 100 101 4 102 6 7]
Thanks for pointing out that I had left allclose out of the Numeric part of the manual. I did it in the MA part and then forgot. I'm fixing it now. BTW: There are changenotes at source forge that are sometimes ahead of the manual.
Original Message From: numpydiscussionadmin@lists.sourceforge.net [mailto:numpydiscussionadmin@lists.sourceforge.net]On Behalf Of John J. Lee Sent: Friday, August 17, 2001 6:36 AM To: Huaiyu Zhu Cc: numpydiscussion@lists.sourceforge.net Subject: Re: [Numpydiscussion] Subarray with with arbitrary index?
On Thu, 16 Aug 2001, Huaiyu Zhu wrote:
Hi,
Is it possible to assign to a subarray with arbitrary index?
Suppose I have three arrays
a = arange(8) b = array([2, 3, 5]) c = arange(3)+100
I want a function f, such that calling f(a, b, c) would change a to
[0 1 100 101 4 102 6 7]
f = Numeric.put f(a, b, c)
put used to be in Python, but it's been in C since some release 17.x.x, I think.
I have a sinking feeling that I must have missed something (no interpreter here to check it works)...
BTW, a week ago I noticed that I had reinvented the wheel in rewriting, in an uglier and less efficient form, Numeric.allclose (hope I got the name right). As far as I can see, it isn't listed in the manual. Did I miss it? All it would need is the docstring copying over.
John
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Following up to an earlier discussion, I've written up some wrapper functions for subarrays. The 'takes' function only works for 2d arrays, but the 'puts' function works for arbitrary array. Hopefully something like this can be included in Numeric module.
Huaiyu Zhu
""" Wrapper functions for dealing with arbitrary subarrays.
Example: addeqs(x, [[0,2], [1,3,4], y), would add (2,3)array y to the (2,3)subarray of x comprised of rows 0, 2 and columns 1, 3, 4.
A more natural notation of addeqs(x, ij, y) would be x[ij] += y, but seems difficult to do with current numpy. (How to let slice handle lists?)
"""
from Numeric import *
def puts(x, irows, icols, v): """ puts(x, i, j, v): Put v in subgrid of 2d array x given by i, j. """ nrow, ncol = x.shape if irows is None: irows = arange(nrow) if icols is None: icols = arange(ncol) if len(shape(icols)) == 1: icols = icols[:ncol] if len(shape(irows)) == 0 or len(shape(icols)) == 0: ii = irows*ncol + icols v1 = v else: ii = (irows*ncol)[:, NewAxis] + icols[NewAxis, :] v1 = reshape(v, shape(ii)) put(x, ii, v1)
def takes(x, I): """ takes(x, I): Takes a subgrid from array x. I is a list of list of subindices. """ for i in xrange(len(I)): ii = I[i] if ii is not None: x = take(x, ii, i) return x
def addeqs(x, ij, y): """ Simulates x[ij] += y, where ij can be arbitray subarray. """ i, j = ij puts(x, i, j, takes(x, ij) + y)
if __name__ == "__main__": a5 = arange(5) a2 = arange(2) a3 = arange(3) d = array([a3, a3+3]) print d; print
b = array([a5, a5+5, a5+10, a5+15]); print b; print c = b.copy(); puts(c, None, 3, a5+1000); print c; print c = b.copy(); puts(c, a2*2, 3, a5+1000); print c; print c = b.copy(); puts(c, 2, a2*2, a5+1000); print c; print c = b.copy(); puts(c, a2*2+1, a3*2, d+1000); print c; print c = b.copy(); d1 = takes(c, (a2*2+1, a3*2)) c1 = c print d1; print puts(c, a2*2+1, a3*2, d+1000); print c; print puts(c, a2*2+1, a3*2, d1); print c; print
addeqs(c, (a2*2+1, a3*2), d1*0+100); print c; print print c1; print d1 += 20; print c; print # Alas, this does not change c
d2 = takes(c, (a2*2+1, None)) print d2; print print shape(c), shape(a2), shape(d2) addeqs(c, (a2*2+1, None), d2) print c; print
""" The expected results are [[0 1 2] [3 4 5]]
[[ 0 1 2 3 4] [ 5 6 7 8 9] [10 11 12 13 14] [15 16 17 18 19]]
[[ 0 1 2 1000 4] [ 5 6 7 1001 9] [ 10 11 12 1002 14] [ 15 16 17 1003 19]]
[[ 0 1 2 1000 4] [ 5 6 7 8 9] [ 10 11 12 1001 14] [ 15 16 17 18 19]]
[[ 0 1 2 3 4] [ 5 6 7 8 9] [1000 11 1001 13 14] [ 15 16 17 18 19]]
[[ 0 1 2 3 4] [1000 6 1001 8 1002] [ 10 11 12 13 14] [1003 16 1004 18 1005]]
[[ 5 7 9] [15 17 19]]
[[ 0 1 2 3 4] [1000 6 1001 8 1002] [ 10 11 12 13 14] [1003 16 1004 18 1005]]
[[ 0 1 2 3 4] [ 5 6 7 8 9] [10 11 12 13 14] [15 16 17 18 19]]
[[ 0 1 2 3 4] [105 6 107 8 109] [ 10 11 12 13 14] [115 16 117 18 119]]
[[ 0 1 2 3 4] [105 6 107 8 109] [ 10 11 12 13 14] [115 16 117 18 119]]
[[ 0 1 2 3 4] [105 6 107 8 109] [ 10 11 12 13 14] [115 16 117 18 119]]
[[105 6 107 8 109] [115 16 117 18 119]]
(4, 5) (2,) (2, 5) [[ 0 1 2 3 4] [ 0 0 0 0 0] [10 11 12 13 14] [ 0 0 0 0 0]] """
participants (3)

Huaiyu Zhu

John J. Lee

Paul F. Dubois