Question

I have a txt file containing on each line 2 values separated by a space:

x1 y1
x2 y2
x3 y3
...
xn yn

I want to get another file containing:

x1 y1
x2 y1+y2
x3 y1+y2+y3
...
xn y1+y2+y3+...+yn

What is the quickest (I mean easiest) way to do this in python ?

Answer 1

This will get you started.

Given data.txt:

1 1
2 2
3 3
4 4

and this code snippet:

with open('data.txt') as inf:
    ysum = 0
    for line in inf:
        line = line.split()
        x, y = [float(i) for i in line]
        ysum += y
        print x, ysum

will give you (using float() above):

1.0 1.0
2.0 3.0
3.0 6.0
4.0 10.0

On the other hand, if you wanted the lines with the +:

with open('data.txt') as inf:
    yline = []
    for line in inf:
        line = line.split()
        x = int(line[0])
        yline = '+'.join(yline + [(line[1])])
        print x, yline
        yline = [yline]

will give you (using int() this time):

1 1
2 1+2
3 1+2+3
4 1+2+3+4

I suspect the above code, esp the 2nd one, could probably be streamlined/optimized more, but should be sufficient to get you started.

You still will have adjust the conversion from string to appropriate type (float or int) and also create the output file and write to it in the format you prefer. These are details you can best decide.