python max of list of arrays with lists [duplicate]

Question

Possible Duplicate:
python max of list of arrays

I have a list of arrays like:

a = [array([ [6,2] , [6,2] ]),array([ [8,3],[8,3] ]),array([ [4,2],[4,2] ])]

I tried max(a) which returns the following error:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

I want it to return either a list or array like:

In: max(a)
Out: [[8,3],[8,3]]

I don't want to convert the inner arrays to list, because the size of the list is very big. Also I purposefully created like that to perform array operations.

And your accepted answer from stackoverflow.com/questions/13227578/… isn't suitable...? — Jon Clements
– Jon Clements, Commented Nov 5, 2012 at 9:52

alexvassel · Accepted Answer · 2012-11-05 09:58:08Z

1

In your example you can do something like this:

max(a, key=lambda i: i[0][0])

Depends on what result do you want (what key to use for sorting) you probably have to 'play' with indexes.

http://docs.python.org/2/library/functions.html#max

answered Nov 5, 2012 at 9:58

alexvassel

10.8k3 gold badges33 silver badges32 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Jon Clements · Accepted Answer · 2012-11-05 10:03:45Z

0

Anyay, not sure how your previous answer wasn't sufficient, but if you're dealing with numpy arrays, then why isn't the whole lot an array, instead of a list of arrays... Then just use the appropriate numpy function:

from numpy import array

a = array(
    [
    array([ [6,2], [6,2] ]),
    array([ [8,3], [8,3] ]),
    array([ [4,2], [4,2] ])
    ]
)

print a.max(axis=0)
#[[8 3]
# [8 3]]

edited Nov 5, 2012 at 10:03

answered Nov 5, 2012 at 9:57

Jon Clements

143k34 gold badges254 silver badges288 bronze badges

1 Comment

Thiru Over a year ago

This works exactly for my case. Thank you very much.

jcr · Accepted Answer · 2012-11-05 10:01:17Z

0

what about:

max(a, key=lambda x:np.max(x))
# array ([[8, 3], [8, 3]])

please note: the fist max is 'normal max' and the second one is np's max... the logic here is that max uses np.max as it's key for comparison, np.max returns the highest number in the array.

is that what you want?

answered Nov 5, 2012 at 10:01

jcr

1,0356 silver badges18 bronze badges

Collectives™ on Stack Overflow

python max of list of arrays with lists [duplicate]

3 Answers 3

Comments

1 Comment

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Linked

Related