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Equivalent of 'ismember' from Matlab in Python?

Answer 1

+2 A:

you can get your vector as

same_rows = [a == b for a,b in zip(A, B)]

Note that this will yield True and False instead of 1 and 0 but bool is subclassed from int and True == 1 and False == 0.

to get the max row where this occurs, you can just use

max_row = next(i for i, row in enumerate(reversed(same_rows)) if row == True)

If you want the number of rows that they have in common, you can just use

same_count == sum(same_rows)

Note that this is all for python and assumes that matrices are lists of lists or tuples or tuples of lists or tuples. HTH.

aaronasterling 2010-09-29 18:48:47

or you could just use `map( eq, A, B)` using `eq` from `operator`, also note in Python 3.x that bool is no longer an int but it's own type.

wheaties 2010-09-29 18:52:57

@wheaties, good looking out. updated.

aaronasterling 2010-09-29 19:00:35

@wheaties: bool is still an int, in Python 3. In fact, `issubclass(bool, int)` returns True. You can have a look at the full discussion: http://stackoverflow.com/questions/2764017/is-false-0-and-true-1-in-python-an-implementation-detail-or-guaranteed-by-t

EOL 2010-09-29 19:16:53

@EOL better looking out ;) updated again

aaronasterling 2010-09-29 19:47:27

@EOL I stand corrected.

wheaties 2010-09-29 19:47:59

Note that same_rows = [a == b for a,b in zip(A, B)], gives me yield only True where the rows are equal only at corresponding rows (e.g a[0,:] = b[0,:]) but i need to find all the positions where a row of a is in b.

Cristina 2010-10-01 13:48:03

Kenny, yes I am using Numpy

Cristina 2010-10-01 13:48:23

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Equivalent of 'ismember' from Matlab in Python?

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