Using python for loop to average data

Question

I have a data set that contains 20 years of monthly averages in a numpy array with dimensions (1x240). I'm trying to write a function to spit out the yearly averages. I've managed to do it (I believe), using a for loop, but when I stick the exact same code into a function, it only gives me the first of what should be 20 values.

def yearlymean_gm(gm_data):
    data= np.load(gm_data)
        for i in range (0,20):
        average= data[i*12:i*12+12].sum()/12
        print average
        return average

gm_data is the name of the file.

When I simply manually enter

data= np.load(gm_data)
for i in range (0,20):
    average= data[i*12:i*12+12].sum()/12
    print average
    return average

it successfully reads out the 20 values. I'm pretty sure I just don't quite understand how for loops work in the context of functions. Any explanation (and a fix, if possible), would be awesome.

Secondly, I would love to have these values fed into an numpy array. I tried

def yearlymean_gm(gm_data):
    data= np.load(gm_data)
    average = np.zeroes(20)  
    for i in range (0,20):
        average[i]= data[i*12:i*12+12].sum()/12
        print average
        return average

but this gives me a long, wacky, list. Help on this would be cool too. Thanks!

I'm sure this is a duplicate but I can't find one. You have your return inside your for loop body so it only completes one iteration. Then the function is over so the rest of your loop is kaput. — Two-Bit Alchemist
– Two-Bit Alchemist, Commented Aug 17, 2016 at 17:10
Something's off with the indentation in your examples. Also, the second block of code contains a return but it's not in a function. — roganjosh
– roganjosh, Commented Aug 17, 2016 at 17:10
@Two-BitAlchemist I'm sure there's plenty but they never have a title that makes it easy to track down :) Indentation is invalid though, so I'm not sure we can confirm that this is the cause. — roganjosh
– roganjosh, Commented Aug 17, 2016 at 17:12
An aggregate dataset via pandas might give you the results your looking for (and wouldn't require iterative logic). I can provide additional details if you'd like - just let me know. — Sevyns
– Sevyns, Commented Aug 17, 2016 at 17:14
@Sevyns he's on the right track for what he wants to calculate... he just needs to unindent his return statement — Aaron
– Aaron, Commented Aug 17, 2016 at 17:15

Andrew · Accepted Answer · 2016-08-17 17:44:58Z

5

Why not avoid the "for" loop altogether?

def yearlymean_gm(gm_data):
    data = np.load(gm_data)
    data = data.reshape((12, 20))
    print data.mean(axis=1)
    return data.mean(axis=1)

answered Aug 17, 2016 at 17:44

Andrew

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Aaron · Accepted Answer · 2016-08-17 17:16:33Z

1

here's what you need...

def yearlymean_gm(gm_data):
    data= np.load(gm_data)
    average = np.zeroes(20)  
    for i in range (0,20):
        average[i]= data[i*12:i*12+12].sum()/12
        print average
    return average  #don't return until the loop has completed

answered Aug 17, 2016 at 17:16

Aaron

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