Converting output into a numpy array

Question

I am facing the following issue. I have 4 data files (Data_1...Data_4) and I am trying to get a count of the number of items in column 2 which are less than or equal to 5. My following code does that job.

import numpy as np
filelist=[]
for i in list(range(1,5)):
    filelist.append("/Users/Hrihaan/Desktop/Data_%s.txt" %i)
for fname in filelist:
    data=np.loadtxt(fname)
    z=data[:,1]
    count= len([i for i in z if i <= -5]) # output 5 3 0 9
    x= np.array(count)
    Average=np.mean(x)
    print(Average)

But I am stuck on how to deal with the output (5,3,0,9), I want to create an array from the output (count) to do simple mathematical calculations such as finding mean or median.So the mean should be (5+3+0+9/4 = 4.25) but when I tried the print(average), I am getting the same output 5 3 0 9, not the mean.

Any help would be greatly appreciated.

looks like you need to accumulate count in a list in your for frname loop then turn that into an array outside/after the loop (remove the indentation) — f5r5e5d
– f5r5e5d, Commented Jan 13, 2018 at 1:18

M472 · Accepted Answer · 2018-01-13 01:18:46Z

2

Instead of creating an array for every cycle in the loop, first create a list and convert this list into an array after the loop has finished.

import numpy as np
filelist=[]
for i in list(range(1,5)):
    filelist.append("/Users/Hrihaan/Desktop/Data_%s.txt" %i)

counts = []
for fname in filelist:
    data=np.loadtxt(fname)
    z=data[:,1]
    count= len([i for i in z if i <= -5]) # output 5 3 0 9
    counts.append(count)

x = np.array(counts)
Average=np.mean(x)
print(Average)

answered Jan 13, 2018 at 1:18

M472

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2 Comments

Hrihaan Over a year ago

Thanks a lot, I have used this procedure before, trying out for something within the loop.

StayFoolish Over a year ago

@Hrihaan I think this is the best answer close to what you want. Your loop only get one count each step, you can't average one value in a loop. you have to gather all the counts first, then do an average operation.

François M. · Accepted Answer · 2018-01-13 01:18:48Z

1

I'm not sure I understand what you're asking, and your code can't be reproduced, as we don't have your files.

But if I understand right, you should remove len() from your code :

for fname in filelist:
    #...
    count = [i for i in z if i <= -5]
    count = [5, 3, 0, 9] # for instance
    x = np.array(count) # x will output: array([5, 3, 0, 9])
    Average = np.mean(x) 
    print(Average) # will print: 4.25

answered Jan 13, 2018 at 1:18

François M.

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2 Comments

Hrihaan Over a year ago

Thanks, but cutting down the len() will basically give me all the values from that column which are less than or equal to -5, I just need the count of values that meet that criteria and create the output from the counts of the 4 individual data files.

François M. Over a year ago

The important part in my answer is "your code can't be reproduced" ;). Moreover len() will always return an int afaik, so the comment in your code is unclear. @M472's answer might be what you are looking for, though.

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