Python equivalent of array of structs from MATLAB

Question

I am familiar with the struct construct from MATLAB, specifically array of structs. I am trying to do that with dictionary in Python. Say I have a initialized a dictionary:

samples = {"Name":"", "Group":"", "Timeseries":[],"GeneratedFeature":[]}

and I am provided with another dictionary called fileList whose keys are group names and each value is a tuples of file-paths. Each file path will generate one sample in samples by populating the Timeseries item. Further some processing will make GeneratedFeature. The name part will be determined by the filepath.

Since I don't know the contents of fileList a priori, in MATLAB if samples were a struct and fileList just a cell array:

fileList={{'Group A',{'filepath1','filepath2'}};{'Group B',{'filepath1', 'filepath2'}}}

I would just set a counter k=1 and run a for loop (with a different index) and do something like:

k=1;
for i=1:numel(fileList)
    samples(k).Group=fileList{i}{1};
    for j=1:numel(fileList{i}{2})
        samples(k).Name=makeNameFrom(fileList{1}{2}{j})
        .
        .
    end
    k=k+1
end

But I don't know how to do this in python. I know I can keep the two for loop approach with

for (group, samples) in fileList:
   for sample in samples:

But how to tell python that samples is allowed to be an array/list? Is there a more pythonic approach than doing for loop?

OMG!! append!

ITA
– ITA

2018-05-15 21:22:23 +00:00
Commented May 15, 2018 at 21:22 — ITA
– ITA, Commented May 15, 2018 at 21:22

I. Amon · Accepted Answer · 2018-05-16 15:10:40Z

1

You could store your dictionary itself in a list and simply append new dictionaries in every iteration of the loop:

samplelist = []
samplelist.append(samples.copy()) % dictionary copy needed when duplicating

Accessing the elements in the list would then work as follows (For example the 'Name' field of the i-th sample):

samples_i_name = samplelist[i]["Name"]

A list of all names would be accessible by a simple list comprehension:

namelist = [samplelist[i]["Name"] for i in range(len(samplelist))]

edited May 16, 2018 at 15:10

answered May 16, 2018 at 6:23

I. Amon

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2 Comments

ITA Over a year ago

Thanks...I am able to access it like you said samplelist[i]["Name"] but what if I wanted all names at once? Python says: TypeError: list indices must be integers or slices, not str when I use [:] notation.

I. Amon Over a year ago

Use a list comprehension (essentially a for loop in one line: namelist = [samplelist[i]["Name"] for i in range(len(samplelist))]

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