Appending arrays by array names

Question

I am working with a function which outputs a numpy array around 600 elements long.

array = function_output()
array.shape # this outputs (600,)

I have to work with around 50 outputs this function. Each output is distinct. The goal is to concatenate each of these arrays together into a list (or numpy array) and then save the results.

I foolishly began labeling each array individually, i.e.

array1 = function_output()
array2 = function_output() 
...

and I then thought I could concatenate this into a list, i.e.

list = [array1, array2, array3, ..., array50]

(1) I don't think there's any way around by naming scheme at first. Each output of the function is unique and should be labeled appropriately

(2) however, it feels foolish to define a list this way, copying and pasting. Could I somehow use a 'for' statement to iterate over variable names?

unutbu · Accepted Answer · 2015-12-01 02:18:22Z

3

Whenever you have numbered variable names, think of using a list instead:

output = [function_output() for i in range(50)]

Instead of accessing the first array with array1 you would use output[0] instead (since Python uses 0-based indexing.)

To combine the list of arrays into one NumPy array you could then use

array = np.column_stack(output)

array.shape would then be (600, 50).

edited Dec 1, 2015 at 2:18

answered Nov 30, 2015 at 22:45

unutbu

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2 Comments

ShanZhengYang Over a year ago

Unfortunately, I don't think that works. I should make it clearer above, but each function output is unique---I have to input several parameters in order for it to run correctly.

user2357112 Over a year ago

@ShanZhengYang: The inputs should also be in a list, or perhaps streamed from a data file of some sort.

Josh Smith · Accepted Answer · 2015-12-01 05:28:27Z

I'm not entirely sure how your code is set up, but it seems to me you could take advantage of python's locals() or globals() methods. For example:

    from random import choice as rc

    #randomly populate the arrays
    array1 = rc(range(20))
    array2 = rc(range(20))
    array3 = rc(range(20))
    array4 = rc(range(20)) 
    array5 = rc(range(20))
    array5 = rc(range(20))

    unwanted_variable1 = rc(range(20))
    unwanted_variable2 = rc(range(20))

    local_variables = locals()
    local_keys = list(local_variables.keys())
    wanted_keys = [i for i in local_keys if i[0:5] == 'array']
    # sort the wanted keys numerically
    current_order = [int(i[5:]) for i in wanted_keys]
    desired_order = current_order.copy()
    desired_order.sort()
    ordered_keys = [wanted_keys[current_order.index(i)] for i in desired_order]

    my_list = [local_variables[i] for i in ordered_keys if i[0:5] == 'array']

I'm sure this could have been done a little bit cleaner but I think it gets the idea across.

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