Output formatted 2D text with different number of columns and wrapping in Python

Question

I need to print a 2D array such as

a = [[100.0, 200.0, 300.0, 400.0, 500.0, 600.0],
     [700.0, 800.0, 900.0, 1000.0, 1100.0, 1200.0],
     [1300.0, 1400.0, 1500.0, 1600.0, 1700.0, 1800.0]]

to a text file with following format:

row=    1   1.00E+02    2.00E+02    3.00E+02    4.00E+02    5.00E+02
            6.00E+02    
row=    2   7.00E+02    8.00E+02    9.00E+02    1.00E+03    1.10E+03
            1.20E+03        
row=    3   1.30E+03    1.40E+03    1.50E+03    1.60E+03    1.70E+03
            1.80E+03

Now if it was a simple table, there are many good posts and solutions already such as using print('{0:<8} {1:<8} {2:<8} {3:<8} {4:<8}'.format(...) or looping through the i lines and print(*i.split(","), sep = "\n") etc. But the the fact that elements in the array have to be wrapped in 5 columns (for example if the array was 4 x 14, the numbers for each row span three lines but not all the way) and also the fact that the first two columns are missing for some columns makes it to hard for me. I'd rather not use any fancy libraries but normal ones such as Numpy and Pandas are perfectly fine. The widths of the columns can be flexible, I have seen files such as following acceptable too, and the main limitation is 5 column wrapping:

 row=    1   1.50768831520556500E+03   1.61593623564084623E+03   1.72793908252278788E+03   1.84745178229805083E+03   1.89005237234217384E+03
             1.93242770965689124E+03   1.94285107599349976E+03   1.95428167992566091E+03   1.97250548659241736E+03   2.00154699718308871E+03
             2.03838485708810049E+03   2.07823624774815426E+03   2.13405634328665110E+03   1.95456774471011431E+03
 row=    2   1.44364188653061069E+03   1.52792163517318954E+03   1.61391596698350054E+03   1.70333946512927673E+03   1.73425508334279334E+03
             1.76507211642371681E+03   1.77245044015945177E+03   1.78083908332863643E+03   1.79497739305904815E+03   1.81799782545806261E+03
             1.84660527255144098E+03   1.87589773534454025E+03   1.93023915683827636E+03   1.91021293716667878E+03

Do you have any restraints? Do you need to go to a new row in the text file after 5 items? or is it length based. What happens when you have 2 digit row numbers? and are your spaces fixed to 4? or are they tabs? — Freddy Mcloughlan, Jun 22 '22 at 00:45
Yes the restrain is 5 items in columns exactly (no length limitations), but the rows can be as many as required to print the whole array. Each `row = x ` can extend many many rows until `row= x+1` but only in 5 columns. — MathX, Jun 22 '22 at 00:47
Spaces can be variable and can even be tab separated. I think the spacing should be enough for the row numbers but that's a good point. None of my files have so many lines to use up the whole space for me to know if they will cause a problem. I added another example, if it helps. — MathX, Jun 22 '22 at 00:52

Freddy Mcloughlan · Accepted Answer · 2022-06-22T03:21:11.327

You can use list comprehension to split each row of a into sections of <= 5, and format all your numbers with {:.2E} for scientific notation.

This separates by 4 spaces too

with open('output.txt', 'w') as w:
    for i, row in enumerate(a, start=1):
        # Write start
        w.write(f'row=    {i}    ')
        # Get spaces for row overflow
        space = (12 + len(str(i)))*' '
        # Split row into sections of 5
        tempa = [row[i:i+5] for i in range(0, len(row), 5)]
        # Write row and .join sections by newline + spaces
        w.write(
            f'\n{space}'.join(['    '.join([f'{a:.2E}' for a in b]) for b in tempa]))
        w.write('\n')

row=    1    1.00E+02    2.00E+02    3.00E+02    4.00E+02    5.00E+02
             6.00E+02
row=    2    7.00E+02    8.00E+02    9.00E+02    1.00E+03    1.10E+03
             1.20E+03
row=    3    1.30E+03    1.40E+03    1.50E+03    1.60E+03    1.70E+03
             1.80E+03

Display a decimal in scientific notation

How to divide a list into n equal parts, python

Feel free to simply add and delete spacing in the strings if necessary

@MathX No worries . Feel free to reply if you have any questions — Freddy Mcloughlan, Jun 22 '22 at 03:15

Output formatted 2D text with different number of columns and wrapping in Python

1 Answers1