Skipping rows, and saving a row into several arrays during file readings using Python

Question

I have the following data saved in a sample file test.dat:

n x   y   z   c   i1    i2
------------------------------------
1 1.2 3.4 5.6 1.0 111.1 222.2 
2 7.8 9.0 1.2 2.0 333.3 444.4  
3 3.4 5.6 7.8 1.0 555.5 666.6
------------------------------------
I do not need the last line. 

I am trying to do the following steps:

• Open the file and read it.
• Skip the first two lines.
• Save the first 4 columns as an array dist, and save the fifth column as another array c, and ignore the last two columns.
• Skip the last two lines as well.
• print arrays dist and c.

I wrote the following code at the moment:

with open('test.dat', 'r') as f:
    dump = f.readline().strip()
    dump = f.readline().strip()
    array = [ [float(x) for x in line.split()] for line in f]
f.closed

Please tell me how to do this using Python, and ndarray (as I want to do some numerical operation on the data afterwards.) Thank you!

Answer 1

To read the whole file into one array:

out = np.genfromtxt('test.dat', skip_header=2, skip_footer=1, usecols=range(5))

To split it up into two arrays:

dist, c = np.split(out, [4], 1)

or maybe more simply:

dist = out[:, :4]
c = out[:, 4]