Using multiple indicies for arrays in python

Question

I have a simple question about how to use multiple indicies for an array or rec.array. More specifically, I want to isolate the cell(s) in an array which meet multiple stipulations. For example:

import numpy as np
test = np.ones(5)
test_rec = test.view(recarray)
test_rec.age = np.array([0,1,2,1,4])
test_rec.sex = np.array([0,1,1,0,0])

I want to isolate test_rec where test_rec age is 1 AND test_rec.sex is 1, ie:

test_rec[test_rec.age==1 and test_rec.sex==1]

Unfortunately, this does not work.

It appears you are incorrectly creating your recarray.

Swiss
– Swiss

2011-08-04 05:47:31 +00:00
Commented Aug 4, 2011 at 5:47 — Swiss
– Swiss, Commented Aug 4, 2011 at 5:47

HYRY · Accepted Answer · 2011-08-04 05:49:31Z

1

use logical_and() or bitwise_and(), and you can use & operator to do bitwise_and():

test_rec[(test_rec.age==1) & (test_rec.sex==1)]

the brackets is important, because the precedence of & is lower then ==.

answered Aug 4, 2011 at 5:49

HYRY

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Peter Graham · Accepted Answer · 2011-08-04 05:44:06Z

1

age_is_one = test_rec.age == 1
sex_is_one = test_rec.sex == 1
age_and_sex = numpy.logical_and(age_is_one, sex_is_one)
indices = numpy.nonzero(age_and_sex)
test_rec[indices]

See:

numpy logical operations

numpy.nonzero

answered Aug 4, 2011 at 5:44

Peter Graham

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