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How to efficiently output n elements per string from a numpy array

I have a 1-D numpy array which is quite long. I would like to efficiently write it to a file by putting N spaces on each line in the file. I've tried several methods, but both have big problems.

First, I tried resizing the array by N columns. Given a file descriptor, f:

myArray.reshape(-1, N)
for row in myArray:
    print >> f, " ".join(str(val) for val in row)

This was quite efficient, but requires the array to be a multiple of N elements. If the last line only contains one element (and N is more than one), I would only like to print 1 element ... not a crash.

Then I tried printing the counter and inserting a line break after every Nth item:

i = 1
for val in myArray:
    if i < N:
        print >> f, str(val)+" ",
        i+=1
    else:
        print >> f, str(val)
        i = 1

This worked great for any array of length, but was very slow (taking at least 10x more than my first option). I have been dumping many files from many arrays and cannot use this method due to speed.

Any thoughts on an efficient way to accomplish this inference?

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2 answers 


for i in range(0, len(myArray), N):
    print " ".join([str(v) for v in myArray[i:i+N]])
    # or this 
    # print " ".join(map(str, myArray[i:i+N].tolist()))


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You can add try

/ except

to your transform approach to print the last elements in the output file:



myArray.reshape(-1, N)
try:
    for row in myArray:
        print >> f, " ".join(str(val) for val in row)
except: # add the exact type of error here to be on the save side
    # just print the last (incomplete) row
    print >> f, " ".join(str(val) for val in myArray[-1])
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