numpy savetxt: how to save an integer and a float numpy array into the save row of the file

Question

I have a set of integers and a set of numpy arrays, which I would like to use np.savetxt to store the corresponding integer and the array into the same row, and rows are separated by \n.

In the txt file, each row should look like the following:

12345678 0.282101 -0.343122 -0.19537 2.001613 1.034215 0.774909 0.369273 0.219483 1.526713 -1.637871

The float numbers should separated by space

I try to use the following code to solve this

np.savetxt("a.txt", np.column_stack([ids, a]), newline="\n", delimiter=' ',fmt='%d %.06f')

But somehow I cannot figure out the correct formating for integer and floats.

Any suggestions?

Try setting multiple dtypes for you columns source

forgetso
– forgetso

2020-11-17 10:03:01 +00:00
Commented Nov 17, 2020 at 10:03 — forgetso
– forgetso, Commented Nov 17, 2020 at 10:03

ithomas · Accepted Answer · 2020-11-17 10:10:21Z

Please specify what a "set of integers" and "set of numpy arrays" are: from your example it looks as though ids is a list or 1d numpy array, and a is a 2d numpy array, but this is not clear from your question.

If you're trying to combine a list of integers with a 2d array, you should probably avoid np.savetxt and convert to a string first:

import numpy as np

ids = [1, 2, 3, 4, 5]
a = np.random.rand(5, 5)

with open("filename.txt", "w") as f:
    for each_id, row in zip(ids, a):
        line = "%d " %each_id + " ".join(format(x, "0.8f") for x in row) + "\n"
        f.write(line)

Gives the output in filename.txt:

1 0.38325380 0.80964789 0.83787527 0.83794886 0.93933360
2 0.44639702 0.91376799 0.34716179 0.60456704 0.27420285
3 0.59384528 0.12295988 0.28452126 0.23849965 0.08395266
4 0.05507753 0.26166780 0.83171085 0.17840250 0.66409724
5 0.11363045 0.40060894 0.90749637 0.17903019 0.15035594

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