Question

I want to map a function that takes two arguments over two vectors of the same length, taking an argument from each of these vectors. I can do it with one argument:

map(@sqrt, 1:10)
ans = ....

help map gives the following example:

map(@min, A, B)
ans = ...

where A and B are 2 by 2 matrices, and the result matrix is the element-wise minimum. But when I try this example, I get the following error:

A = rand(2,2);
B = rand(2,2);
map(@min, A, B)
error: invalid assignment to cs-list outside multiple assignment.
error: assignment to cell array failed
error: assignment failed, or no method for `<unknown type> = scalar'
error: called from:
error:   C:\Octave\3.2.4_gcc-4.4.0\share\octave\packages\miscellaneous-1.0.9\map.m at line 108, column 21

What am I doing wrong? My system is Win7, 64 bit, and as you can see, my octave version is 3.2.4.

Answer 1

Thanks to this question, I was able to find out that map is being deprecated, and the correct function to use is arrayfun, which works out of the box, both with octave version 3.2.4, which is what I got when downloading a normal windows installer, and with octave version 3.6.2, which I got using cygwin. In version 3.6.2 it even seems that map requires the miscellaneous package, which arrayfun does not.

So I will never know what I did wrong, or if there is a bug (unlikely, given that the function is pretty standard), but my problem was solved by just substituting arrayfun:

A = rand(2,2);
B = rand(2,2);
arrayfun(@min, A, B)
ans = .... % correct answer