Reading 2d array from file in Python

Question

The following code fills a 2d array (grid) with random numbers(0 or 1):

def create_initial_grid(rows, cols):

grid = []
for row in range(rows):
    grid_rows = []
    for col in range(cols):

        if random.randint(0, 7) == 0:
            grid_rows += [1]
        else:
            grid_rows += [0]

    grid += [grid_rows]
return grid

I want to fill the grid from a text file that looks like this:

7
0,0,0,0,0,0,0
0,0,1,0,1,0,0
0,0,1,1,1,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0

I removed your image and wrote it as text. I did this for you, because you are new, but you should do that yourself in the future. See Why not upload images of code on SO when asking a question — zvone
– zvone, Commented Oct 27, 2018 at 18:11

n1tk · Accepted Answer · 2018-10-27 19:11:58Z

1

Other option is to use numpy.loadtxt to read .txt (since you are use the array and matrix format):

data = np.loadtxt("text.txt", delimiter=",",dtype=int , skiprows=1) 
print(data)

Out:
[[0 0 0 0 0 0 0]
 [0 0 1 0 1 0 0]
 [0 0 1 1 1 0 0]
 [0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0]]
Note:

skiprows=1 # parameter for skipping the first line when reading from the file.

dtype=int parameter for reading in the int format (default is float)

edited Oct 27, 2018 at 19:11

answered Oct 27, 2018 at 19:06

n1tk

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Comments

willeM_ Van Onsem · Accepted Answer · 2018-10-27 18:13:07Z

You can read the file, with:

with open('myfile.txt') as f:
    next(f)  # skip the first line
    data = [list(map(int, line.strip().split(','))) for line in f]

Here next(..) will move the cursor to the next line, since the first here contains a 7.

If there is data after the lines, we might want to prevent reading that, and use:

from itertools import islice

with open('myfile.txt') as f:
    n = int(next(f))  # skip the first line
    data = [list(map(int, line.strip().split(','))) for line in islice(f, n)]

For both file fragments here, the result is:

>>> data
[[0, 0, 0, 0, 0, 0, 0],
 [0, 0, 1, 0, 1, 0, 0],
 [0, 0, 1, 1, 1, 0, 0],
 [0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0]]

Fahad Ali Shaikh · Accepted Answer · 2018-10-27 18:14:30Z

0

filesname = "t.txt"

with open(filesname) as f:
    lines = f.read().split()

n = lines[0]
data_lines = lines[1:]

data = [map(int, row.split(",")) for row in data_lines]

print(data)

Hope this helps!

answered Oct 27, 2018 at 18:14

Fahad Ali Shaikh

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1 Comment

jpp Over a year ago

This won't work in Python 3.x where map is a lazy iterator.

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