Question

Really quick question here, some other people helped me on another problem but I can’t get any of their code to work because I don’t understand something very fundamental here.

8000.5   16745     0.1257
8001.0   16745     0.1242
8001.5   16745     0.1565
8002.0   16745     0.1595
8002.5   16745     0.1093
8003.0   16745     0.1644

I have a data file as such, and when I type

f1 = open(sys.argv[1], 'rt')
for line in f1:
    fields = line.split()
    print list(fields [0])

I get the output

['1', '6', '8', '2', '5', '.', '5']
['1', '6', '8', '2', '6', '.', '0']
['1', '6', '8', '2', '6', '.', '5']
['1', '6', '8', '2', '7', '.', '0']
['1', '6', '8', '2', '7', '.', '5']
['1', '6', '8', '2', '8', '.', '0']
['1', '6', '8', '2', '8', '.', '5']
['1', '6', '8', '2', '9', '.', '0']

Whereas I would have expected from trialling stuff like print list(fields) to get something like

[16825.5, 162826.0 ....] 

What obvious thing am I missing here?

thanks!

Answer 1

Remove the list; .split() already returns a list.

You are turning the first element of the fields into a list:

>>> fields = ['8000.5', '16745', '0.1257']
>>> fields[0]
'8000.5'
>>> list(fields[0])
['8', '0', '0', '0', '.', '5']

If you want to have the first column as a list, you can build a list as you go:

myfirstcolumn = []
for line in f1:
    fields = line.split()
    myfirstcolumn.append(fields[0])

This can be simplified into a list comprehension:

myfirstcolumn = [line.split()[0] for line in f1]