Save all values of a variable (in a loop) in another variable in Python

Question

I have a code that I inform a folder, where it has n images that the code should return me the relative frequency histogram.

From there I have a function call:

for image in total_images:
    histogram(image)

Where image is the current image that the code is working on and total_images is the total of images (n) it has in the previously informed folder.

And from there I call the histogram() function, sending as a parameter the current image that the code is working.

My histogram() function has the purpose of returning the histogram of the relative frequency of each image (rel_freq).

Although the returned values are correct, rel_freq should be a array 1x256 positions ranging from 0 to 255.

How can I transform the rel_freq variable into a 1x256 array? And each value stored in its corresponding position?

When I do len *rel_freq) it returns me 256, that's when I realized that it is not in the format I need...

Again, although the returned data is correct...

After that, I need to create an array store_all = len(total_images)x256 to save all rel_freq...

I need to save all rel_freq in an array to later save it and to an external file, such as .txt.

I'm thinking of creating another function to do this...

Something like that, but I do not know how to do it correctly, but I believe you will understand the logic...

def store_all_histograms(total_images):
    n = len(total_images)

    store_all = [n][256]

    for i in range(0,n):
        store_all[i] = rel_freq

I know the function store_all_histograms() is wrong, I just wrote it here to show more or less the way I'm thinking of doing... but again, I do not know how to do it properly... At this point, the error I get is:

    store_all = [n][256]
IndexError: list index out of range

After all, I need the store_all variable to save all relative frequency histograms for example like this:

position:     0   ...  256 
store_all = [
            [..., ..., ...],
            [..., ..., ...],
            .
            .
            .
            n
            ]

Now follow this block of code:

def histogram(path):
    global rel_freq

    #Part of the code that is not relevant to the question...

    rel_freq = [(float(item) / total_size) * 100 if item else 0 for item in abs_freq]

def store_all_histograms(total_images):
    n = len(total_images)

    store_all = [n][256]

    for i in range(0,n):
        store_all[i] = rel_freq

#Part of the code that is not relevant to the question...

# Call the functions
for fn in total_images:
    histogram(fn)

    store_all_histograms(total_images)

I hope I have managed to be clear with the question.

Thanks in advance, if you need any additional information, you can ask me...

"When I do len (rel_freq) it returns me 256, that's when I realized that it is not in the format I need..." what do you expect from a 1x256 array? len is a python builtin. — roganjosh
– roganjosh, Commented Jun 29, 2017 at 18:37
Welcome to stack overflow. A longer question is not necessarily better than a brief one. I have a hard time understanding what is the important part of your question is. Here's a guide to writing great questions: How to Ask — Håken Lid
– Håken Lid, Commented Jun 29, 2017 at 18:46
@roganjosh I need this because I will later put the value of the histograms into the Multilayer Perceptron and see if it is able to classify my images. — whoisraibolt
– whoisraibolt, Commented Jun 29, 2017 at 18:48
That's fine. I perhaps wasn't clear; the len of a 1x256 array will just show 256 so even if it's a numpy array, len will look at it like a (nested if necessary, which it's not here) list. That's not an indication that anything went wrong. As @HåkenLid stated, your question is quite long and that was the first issue I picked up on. — roganjosh
– roganjosh, Commented Jun 29, 2017 at 18:50

Mike Müller · Accepted Answer · 2017-06-29 18:50:37Z

2

Return the result, don't use a global variable:

def histogram(path):
    return [(float(item) / total_size) * 100 if item else 0 for item in abs_freq]

Create an empty list:

store_all = []

and append your results:

for fn in total_images:
    store_all.append(histogram(fn))

Alternatively, use a list comprehension:

store_all = [histogram(fn) for fn in total_images]

edited Jun 29, 2017 at 18:50

answered Jun 29, 2017 at 18:37

Mike Müller

86k21 gold badges174 silver badges165 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

J0hn · Accepted Answer · 2017-06-29 18:37:44Z

1

for i in range(0,n):
    store_all[i+1] = rel_freq

Try this perhaps? I'm a bit confused on the question though if I'm honest. Are you trying to shift the way you call the array with all the items by 1 so that instead of calling position 1 by list[0] you call it via list[1]?

So you want it to act like this?

>>list = [0,1,2,3,4]
>>list[1]
0

answered Jun 29, 2017 at 18:37

J0hn

5805 silver badges19 bronze badges

1 Comment

whoisraibolt Over a year ago

>>list = [[0,0,0,0,...,0,0,0,0], [1,1,1,1,...,1,1,1,1], [2,2,2,2,...,2,2,2,2]] >>list[3] >>[2,2,2,2,...,2,2,2,2] This is how I need it...

Collectives™ on Stack Overflow

Save all values of a variable (in a loop) in another variable in Python

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related