How to add a Numpy Array to a dictionary

Question

How to add two numpy arrays to a dictionary in python ?

a = [[1]
     [3]]

b = [array([[[ 41.,  179.],
             [ 451.,  254.],
             [ 449.,  10.],
             [ 53.,  256.]]], dtype=float32), array([[[ 181.,  313.],
             [  27.,  24.],
             [ 113.,  192.],
             [ 08.,  20.]]], dtype=float32)]

I wish to display a and b as

c = {1: array([[ 41.,  179.],
            [ 451.,  254.],
            [ 449.,  10.],
            [ 53.,  256.]], dtype=float32),
     3: array([[ 181.,  313.],
           [  27.,  24.],
           [ 113.,  192.],
           [ 08.,  20.]], dtype=float32)}

Does the solution have to be scalable?

Joe Iddon
– Joe Iddon

2017-11-12 19:06:23 +00:00
Commented Nov 12, 2017 at 19:06 — Joe Iddon
– Joe Iddon, Commented Nov 12, 2017 at 19:06
Yes, it has to be.

vulcanrs
– vulcanrs

2017-11-12 19:08:10 +00:00
Commented Nov 12, 2017 at 19:08 — vulcanrs
– vulcanrs, Commented Nov 12, 2017 at 19:08

dsm · Accepted Answer · 2017-11-12 19:08:02Z

5

c = dict(zip(a[:,0], b)) would turn your a and b variables into a dictionary. I'm not sure whether that's what you're looking for, though.

edited Nov 12, 2017 at 19:08

answered Nov 12, 2017 at 18:59

dsm

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2 Comments

vulcanrs Over a year ago

It returns an error saying - TypeError: unhashable type: 'numpy.ndarray'

dsm Over a year ago

Oh right, I didn't notice the exact form of your a. I assume what you meant there was a = np.array([[1],[3]]). If that's the case, dict(zip(a[:,0], b)) should do it.

Joe Iddon · Accepted Answer · 2017-11-12 19:12:40Z

2

Using a dictionary comprehension:

I assume you meant to define a as:

a = [1, 3]

then you can get c with:

c = {e: b[i] for i, e in enumerate(a)}

which gives the intended output of:

{1: array([[[  41.,  179.],
    [ 451.,  254.],
    [ 449.,   10.],
    [  53.,  256.]]], dtype=float32),
 3: array([[[ 181.,  313.],
    [  27.,   24.],
    [ 113.,  192.],
    [   8.,   20.]]], dtype=float32)}

If you actually only have a as a list of an element as in [[1], [3]], you can do:

a = [i[0] for i in a]
#[[1], [3]] --> [1, 3]

edited Nov 12, 2017 at 19:12

answered Nov 12, 2017 at 19:07

Joe Iddon

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2 Comments

vulcanrs Over a year ago

Still gives an error TypeError: unhashable type: 'numpy.ndarray'

vulcanrs Over a year ago

Am sorry, works perfect !! I made an error typing your code.

en_lorithai · Accepted Answer · 2017-11-12 19:17:15Z

small mistake in c, needs a comma between the two inner lists (are nested lists necessary here?)

Anyways, here is a solution that gives the desired output you want.

import numpy as np
c = {}

a = [[1],[3]]

b = [np.array([[[ 41.,  179.],
             [ 451.,  254.],
             [ 449.,  10.],
             [ 53.,  256.]]], dtype=np.float32), np.array([[[ 181.,  313.],
             [  27.,  24.],
             [ 113.,  192.],
             [ 08.,  20.]]], dtype=np.float32)]

for i in range(len(a)):
    c[a[i][0]] = b[i]

Create a dictionary first (c), then use the values in your nested list a as keys. for each of those keys assign the array in your list b at the same index (i). Do note that this requires that the indexes of a corresponds to the same positions in b.

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