Python array multiply

Question:

hh=[[82.5], [168.5]]
N=1./5
ll=N*hh

What I’m doing wrong? I received error :

“can’t multiply sequence by non-int of
type ‘float'”

I try to add float(), but this is not solve my problem;

I need to multiply each element in array…
thanks to all

**Ok thanks for idea for number * array, but how to multiply array*array, I tried same as number*array, but have problems:

EDIT 2:**

hh=[[82.5], [168.5]]
N=zip(*hh)
ll = [[x*N for x in y] for y in hh]

???

Asked By: thaking

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Source

Answers:

When you multiply a sequence by X in Python, it doesn’t multiply each member of the sequence – what it does is to repeat the sequence X times. That’s why X has to be an integer (it can’t be a float).

What you want to do is to use a list comprehension:

hh = [[82.5], [168.5]]
N  = 1.0 / 5
ll = [[x*N for x in y] for y in hh]
Answered By: Boaz Yaniv

Well in Python you can do this:

>>> [2] * 3
[2, 2, 2]

This requires an int type.

What you are looking for is something a kin to map or a list comprehension.

>>> list(map(lambda x: x * 2, [2, 2]))
[4, 4]
>>> [x * 2 for x in [2, 2]]
[4, 4]

You can also generator comprehension to do it lazily.

(x * 2 for x in [2, 2])

Or you can do it a bit Haskellish (albeit without the elegance):

>>> import operator
>>> from functools import partial, reduce
>>> add = partial(operator.mul, 2)
>>> list(map(add, [2,2]))
[4, 4]
Answered By: Skurmedel

You can also use the numpy array for multiplying the numbers in the array.

>>> hh = numpy.asarray([[82.5], [168.5]])
>>> N = 1.0/5
>>> ll = N*hh
>>> ll
array([[ 16.5],
       [ 33.7]])
Answered By: SiggyF