Question

This is my first post even though I’ve been reading SO for a while.
I’m a Python beginner and I’d need your help.
I’m processing a very big file (more than 2 million of lines) but I’ll show you a much smaller example (24 lines rather than 74513). So let’s say I’ve got 24 lines, each one with a floating point number, after that 3 numbers on the same line, then again 24 lines, line with 3 numbers and so on for 29 times.

56.71739
56.67950
56.65762
56.63320
56.61648
56.60323
56.63215
56.74365
56.98378
57.34681
57.78903
58.27959
58.81514
59.38853
59.98271
60.58515
-1.00000
56.09566
56.05496
56.02777
56.00158
55.98341
55.96830
55.99615
          1            1          1
56.34692
56.70977
57.15187
57.64234
58.17782
58.75118
59.34534
59.94779
-1.00000
55.47366
55.42963
55.39739
55.36958
55.35020
55.33404
55.36098
55.47148
55.71110
56.07384
56.51588
57.00632
57.54180
58.11517
58.70937
         2            1           1

It’s quite easy to create an array with the first 24 lines:

import numpy

def ttarray_tms (traveltimes):
    '''It defines the 3-D array, organized as I want.'''
    with open (traveltimes, 'r') as file_in:
        newarray = file_in.readlines()
        ttarray = np.array(newarray)
        ttarray.shape = (2,3,4)
        ttarray = np.swapaxes(ttarray,1,2)
        ttarray = np.swapaxes(ttarray,0,2)
        return ttarray

PLEASE NOTE: There’s no blank line between each number. It’s a simple colon-vector file. For some reason I had to post like that.
What I want is to basically get 29 arrays, so I should loop over the 24 lines and get an array, then loop again over the next 24 lines (jumping the line with 3 numbers, I don’t really need them) and get another array and so on. I think my main problem is how to skip the line with the 3 numbers and start again a new loop for a new array.

Have you got any good idea?

Thanks very much!

Answer 1

You can use readline() to read a single line 24 times then use another readline() to skip a line and so on.

With your code:

import numpy

def mk_array(elems):
    '''Makes the nparray from an array of 24 numbers'''
    ttarray = np.array(elems) # perhaps [ float(a) for a in elems ] is needed
    ttarray.shape = (2,3,4)
    ttarray = np.swapaxes(ttarray,1,2)
    ttarray = np.swapaxes(ttarray,0,2)
    return ttarray

def ttarray_tms(traveltimes):
    '''It defines the 3-D array, organized as I want.'''
    arrays = list()
    with open (traveltimes, 'r') as file_in:
        ret = "." # force the loop
        while ret != "":
            newarray = [ file_in.readline() for i in range(24) ]
            ret = file_in.realine()
            if ret != "": # avoid an empty array
                ttarray = mk_array(newarray)
                arrays.append(ttarray)       
    return arrays

Not tested.