Equivalent of numpy.where() value choice parameters

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Andrew Glick
Andrew Glick 2021-10-10
评论： Jan 2021-10-13
I am trying to emulate the behavior of the Numpy function numpy.where() in MATLAB, specifically the optional 2 parameters that allow picking from from other arrays.
I have the following Python code which selects
>>> import numpy as np
>>> x = np.arange(10)
>>> y = np.arange(10) * -0.1
>>> z = np.where(x % 2 == 0, x, y)
>>> print(z)
[ 0. -0.1 2. -0.3 4. -0.5 6. -0.7 8. -0.9]
The function numpy.where() selects between the two arrays, x and y, based on the condition in the first argument.
The best I have been able to do in MATLAB is:
x = 0:9
y = (0:9) * -0.1
z = zeros(size(x))
z(mod(x, 2)!=0) = y(mod(x,2)==0)
z(mod(x, 2)~=0) = y(mod(x,2)~=0)
Is there a better way of doing this?

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采纳的回答

Jan
Jan 2021-10-10
Your code looks almost fine:
x = 0:9
y = (0:9) * -0.1
z = zeros(size(x));
z(mod(x, 2) == 0) = x(mod(x,2) == 0);
% ^ not ! ^ not y
z(mod(x, 2) ~= 0) = y(mod(x,2) ~= 0);
More efficient:
z = x;
m = (mod(x, 2) ~= 0);
z(m) = y(m);
  2 个评论
Andrew Glick
Andrew Glick 2021-10-11
Thanks!
(I'm a bit embarrassed that I made two obvious typos in the Matlab code. Oops! Thanks for catching those!)
Jan
Jan 2021-10-13
Typos are then beloved companion of the programmer. They emerge from expressing thoughts by fingers. As soon as we omit the keyboards by developping a mind controlled input method, the new device will get a bi-directional interface and monopolistic internet services will project commercials directly in my subconciousness. Therefore I like typos.

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