Python create a dictionary with 'numpy.ndarray'

Question

I have an empty 'numpy.ndarray'

import numpy as np
my_grid =  np.zeros((5, 5))

parse = "max","min","avg"

I wish to create a dictionary where each element of parse is the "Key"

from collections import defaultdict

GridMetric = dict()
for arg in parse:
    GridMetric[arg].append(my_grid)

but i get this error

   Traceback (most recent call last):
  File "<editor selection>", line 3, in <module>
KeyError: 'max'

You can't use a numpy array as the key of a dictionary (just like you can't use a list or other mutable object). — Warren Weckesser
– Warren Weckesser, Commented Mar 3, 2013 at 17:21
Would you give an exact code which produces this error, so that we see exactly what is parse here. — ev-br
– ev-br, Commented Mar 3, 2013 at 17:26
Do you want to create a separate dictionary "for each element of parse" or do you want to create dictionary in which items in parse are keys, and the values are ... what? — ASGM
– ASGM, Commented Mar 3, 2013 at 17:30

ASGM · Accepted Answer · 2013-03-03 17:40:31Z

3

If what you want is a dictionary whose keys are the different elements of the list called parse and whose values are all the same array, then the following changes to your code should work:

import numpy as np
my_grid =  np.zeros((5, 5))

parse = ["max","min","avg"]

d = {}
for arg in parse:
    d[arg] = my_grid

answered Mar 3, 2013 at 17:40

ASGM

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5 Comments

ASGM Over a year ago

What is the problem with this code? You said "you get it" when I wrote "every key (different elements of the list, parse) will have the same value (the same array, my_grid)?" In what way does the code provided not do that for you?

Gianni Spear Over a year ago

i got always Traceback (most recent call last): File "<editor selection>", line 3, in <module> KeyError: 'max' becose i need parse as "max", "min", "avg"

DSM Over a year ago

@Gianni: that's because you imported defaultdict from collections, but aren't using it -- your object is a dict, although it looks like you want defaultdict(list), and so there's none of the default-creation behaviour. You say you want the grid to be the value, but instead you're going to have values which are lists, the first element of which is my_grid.

DSM Over a year ago

@user2074981: I suspect the OP really wants my_grid.copy(), even though I agree that you asked exactly this question -- whether he wanted each value to be the same array -- and he said yes.

Gianni Spear Over a year ago

@DSM It's true. I forgot GridMetric =defaultdict(list) and I made this mistake. Sorry and thanks for your time and help.

sedders123 · Accepted Answer · 2019-07-17 13:56:14Z

1

Try this:

import numpy as np

my_grid =  np.zeros((5, 5))

parse = ["max","min","avg"]


for arg in parse:
    dict(parse=my_grid)

print(d)

edited Jul 17, 2019 at 13:56

sedders123

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answered Jul 17, 2019 at 13:25

Muhammad Umar

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