Python: Create Array Objects Dynamically

Question

I want to dynamically create arrays with variable names from another array. Say that I have:

    Array1 = ['a', 'b', 'c']

I want to now programatically create a new array for each value in Array1 (where I do not know how many values will actually be in Array1 and I do not know the names that will be in there) using the names provided in Array1. So effectively it will give me:

    a = []
    b = []
    c = []

Foreach over master array, and for each element create new array? — Andrew Li, Jun 13 '16 at 20:27
That is correct, and each new array should take the name that is given in the master array. — user3124181, Jun 13 '16 at 20:31
I'm not sure you can dynamically create individual variables like that in python. I defer to greater experts on that. As a compromise and perhaps something more readable create an dictionary of arrays with a, b, c as the keys in the dictionary. — mba12, Jun 13 '16 at 20:32
technically you can do "dynamic variable names" by using dictionary operations on `globals()` but 99.8% of the cases you would do that it would make more sense to just define your own dictionary. (the only exception I can think of is when you want to monkey patch your code) — Tadhg McDonald-Jensen, Jun 13 '16 at 20:33

score 4 · Accepted Answer · answered Jun 13 '16 at 20:31

4

When you do Array1 = [a,b,c], you lose any information about the names of the variables you used to instantiate the array, so I'll assume you meant Array1=['a','b','c']. In Python, we generally use a dictionary to solve issues related to this. Using a dictionary, we can have a mapping from 'a' to an empty list like so:

Array1 = ['a','b','c']
dicty = {}
for i in Array1:
    dicty[i] = []

If this doesn't help you solve your problem, please give me more information about what problem you are trying to solve.

answered Jun 13 '16 at 20:31

Brian

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Yes, that is what I intended, I will change my original question to include the single quotes in Array1=['a','b','c']... Thank you for your solution, this works. – user3124181 Jun 13 '16 at 20:33
1

Good work @Brian, addressing the confusion while still providing a solution to the problem :) +1 – salezica Jun 13 '16 at 20:34

score 0 · Answer 2 · answered Jun 13 '16 at 20:38

So there are a few hypotheses that must be satisfied. Mainly, if Array1 has multiple entries that are equal, then you can't have different arrays for them--for example, if a == b evaluates to True, then you must assign them both the same arrays. Secondly, why not just keep a dictionary with the names of the corresponding arrays:

names_dict = {} ## names_dict[a] = (0,0), names_dict[b] = (1,0), ...
new_arrays = {}
for i in Array1.shape()[0]: 
    for j in Array1.shape()[1]:
         names_dict[Array1[i][j]] = (i,j)
         new_arrays[(i,j)] = np.array(...) ## whatever array you want to create goes in the "..."

new_arrays[names_dict[a]] will evaluate to the array for element a

Python: Create Array Objects Dynamically

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