Python dictionary to NumPy conversion

Question

I am converting a Python dictionary to NumPy array.

import numpy as np

myDict = {
        1: "AAA",
        2: "BBB",
        3: "CCC",
        4: "AAA",
        5: "BBB"
        }

myNumPyArray = np.asarray(myDict, dtype=dict, order="C")

print(myNumPyArray)

Output

{1: 'AAA', 2: 'BBB', 3: 'CCC', 4: 'AAA', 5: 'BBB'}

Why is it showing the dictionary in the output?

You could do myNumPyArray = np.array(list(myDict.items())) instead. — Ari Cooper-Davis
– Ari Cooper-Davis, Commented Jul 18, 2019 at 8:30
the issue is, it's an array of a dict. Numpy cannot know how you want the dict to be inferred, also take a look at docs. Use .items.() or .values() on the dict before calling numpy array on it — Paritosh Singh
– Paritosh Singh, Commented Jul 18, 2019 at 8:32
What output do you expect? The manual says you should pass "lists, lists of tuples, tuples, tuples of tuples, tuples of lists and ndarrays" for the first argument. — Leporello
– Leporello, Commented Jul 18, 2019 at 8:32

tstanisl · Accepted Answer · 2019-07-18 09:13:11Z

1

This "fails" because an array containing a single scalar value of type 'object' is created. This scalar value will be a pointer to the dictionary. If you want to transform content of the dictionary to ndarray you can use structured array with 2 fields. One for integer index, other for value as a fixed length string. Using np.fromiter is a fast method because it avoids creation of any temporary objects.

np.fromiter(myDict.items(), dtype='i4,U3', count=len(myDict))

edited Jul 18, 2019 at 9:13

answered Jul 18, 2019 at 9:01

tstanisl

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