# [Numpy-discussion] multi-comparison expressions

Mon Oct 6 14:49:20 CDT 2008

```a < b < c

is equivalent to:

(a < b) and (b < c)

If you wand an element-wise operation you have to use the & operator, so the expression is:

(a > 2) & (a < 5)

-----הודעה מקורית-----
מאת: numpy-discussion-bounces@scipy.org בשם John
נשלח: ב 06-אוקטובר-08 21:32
אל: numpy-discussion@scipy.org
נושא: [Numpy-discussion] multi-comparison expressions

hi,

why does the ValueError appear below, and how can i make that 2<a<5
expression work when a is an array?

thanks.

>>> from numpy import reshape,arange
>>> a=reshape(arange(9),(3,3))
>>> a
array([[0, 1, 2],
[3, 4, 5],
[6, 7, 8]])
>>> 2<a
array([[False, False, False],
[ True,  True,  True],
[ True,  True,  True]], dtype=bool)
>>> a<5
array([[ True,  True,  True],
[ True,  True, False],
[False, False, False]], dtype=bool)
>>> 2<a<5
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: The truth value of an array with more than one element is
ambiguous. Use a.any() or a.all()

nor does it work with constant arrays:

>>> from numpy import zeros
>>> twos=zeros(a.shape)+2
>>> fives=zeros(a.shape)+5
>>> twos<a
array([[False, False, False],
[ True,  True,  True],
[ True,  True,  True]], dtype=bool)
>>> a<fives
array([[ True,  True,  True],
[ True,  True, False],
[False, False, False]], dtype=bool)
>>> twos<a<fives
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: The truth value of an array with more than one element is
ambiguous. Use a.any() or a.all()

but it works with builtin numbers:

>>> b=3
>>> 2<b<5
True

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