Extracting values of a key from an array of dictionaries

Question

I want to read from a .npy file to do some signal processing tasks but during this task I received this error:

IndexError: only integers, slices (:), ellipsis (...), numpy.newaxis (None) and integer or boolean arrays are valid indices

this is my code:

import numpy as np
import matplotlib.pyplot as plt


file  = '/signal/data.npy'
d = np.load(file,allow_pickle=True,encoding = 'latin1')

d['soma'][0]

There are same questions but I could not use them to solve this one.So can anyone help me to fix It? Thanks

This the error:

This is part of my data( d is equal to res):

Please include your data.npy so it is reproducible. Thank you. — Ehsan
– Ehsan, Commented Apr 16, 2020 at 4:50
So your array includes bunch of dictionaries. Are you looking to extract ALL elements that include keys ["results"]["lfp"] for example, or a specific element with that key? — Ehsan
– Ehsan, Commented Apr 16, 2020 at 5:09
res is a object dtype array containing dictionaries. res[0] is one of those dictionaries. res[0]['soma'] should work. The indexing order matters. — hpaulj
– hpaulj, Commented Apr 16, 2020 at 6:44

jdragon · Accepted Answer · 2020-04-23 06:14:08Z

2

your data consists of arrays of dictionaries. for each array you have some keys with its values. the solution as @ hpaulj said is:

   res[array_index]["your_key"]

edited Apr 23, 2020 at 6:14

answered Apr 23, 2020 at 5:43

jdragon

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Ehsan · Accepted Answer · 2020-04-16 06:13:54Z

2

You have a numpy array d and you are trying to access e.g. "soma" index which is not possible. Numpy indexing rule is:
only integers, slices (:), ellipsis (...), numpy.newaxis (None) and integer or boolean arrays are valid indices.

If your numpy array includes dictionaries, you need to extract dictionaries. d['soma'] does not extract elements of numpy array.
This loops over array d and extracts the first element of values of key 'soma' for all dictionaries in d that has key 'soma':

lfp = [i['soma'][0] for i in d if 'soma' in i]

And if it is a dataframe instead of numpy array, try:

d = pd.read_pickle(file)

edited Apr 16, 2020 at 6:13

answered Apr 16, 2020 at 4:55

Ehsan

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2 Comments

Ehsan Over a year ago

@Mhasa87 Edited the post. Your picture does not include an example that has key results. So I assume its value is also a dictionary that necessarily includes key "lfp". You can include another if statement if you need to check the existence of key in the nested dictionary as well.

MH.AI.eAgLe Over a year ago

Thanks a lot for your help. I think I have some problems, I will change this post.

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