Dump a Numpy Array into a CSV File

Dump a NumPy array into a csv file

numpy.savetxt saves an array to a text file.

import numpy
a = numpy.asarray([ [1,2,3], [4,5,6], [7,8,9] ])
numpy.savetxt("foo.csv", a, delimiter=",")

How can I export my NUMPY array into a CSV or EXCEL file

You can use Pandas to save your NumPy array as CSV (See here)

Suppose numArr is your numpy array. And you can do like this:

import pandas as pd

df = pd.DataFrame(numArr)
df.to_csv('file.csv',index=False)

How to store array of numpy array in csv file?

You could save the numpy array using numpy.save as shown in the docs here. You could save the image name and image path as a .json file (and just make the name of the .npy file the same as the name as the .json file to allow for easier searching).

How to save numpy ndarray as .csv file?

Your array include strings, but np default formatting is for floats.

Try manually setting the format:

np.savetxt(r'g:\test.csv',ab,delimiter=',', fmt=('%s, %f'))

How to write an object typed array into csv file with NumPy?

I think you must use iterations or other libraries e.g. Pandas to do this, because each of the columns will have a different size (in this example we will handle unequal sizes of A and B). So the saved array must be specified as object type if you want to do this by np.savetxt. If you use object typed array to be saved by np.savetxt, it will just fill the first row of the csv file:

A = np.array([2, 4.1, 5], dtype=np.float64)
B = np.array([2, 7, 9, 1], dtype=np.float64)
C = 1
D = 7

Output = np.zeros((1, 4), dtype=object)
Output[0, :] = A, B, C, D

np.savetxt('Output.csv', Output, delimiter=",", fmt='%s')

which will be as:

I don't think if it can be good handled just by NumPy, and will be better to try by other libraries such as Pandas or … or use iterations to open the csv file and import in it. But if you want to use NumPy for doing so (just for figuring out how to do this work by NumPy), it can be achieved by padding to equalize the arrays' sizes in indirect way. For this aim, we must find maximum length of the A and B to pad the arrays to that length. I filled the padded indices by np.nan in this example and then removed it for the output:

max_len = max(A.shape[0], B.shape[0])

A_pad = np.pad(A, (0, max_len - A.shape[0]), constant_values=(np.nan,))
B_pad = np.pad(B, (0, max_len - B.shape[0]), constant_values=(np.nan,))
C_pad = np.pad(np.array([C], dtype=np.float64), (0, max_len - 1), constant_values=(np.nan,))
D_pad = np.pad(np.array([D], dtype=np.float64), (0, max_len - 1), constant_values=(np.nan,))

Output = np.array([A_pad, B_pad, C_pad, D_pad]).T
Output = Output.astype(str)
Output[Output == 'nan'] = ''

np.savetxt('Output.csv', Output, delimiter=",", fmt="%s")

Saving a list containing a numpy array in CSV format in Python

In your code, you are using the file to write your lines rather than the csv writer. Use the csv writer with the writerow function to write a single row to the CSV file:

with open('Data_sigma.csv', 'w') as f:
     writer = csv.writer(f)
     writer.writerow(sigma1[0])

Note, as sigma1 is a list containing the NumPy array, we have written out sigma1[0]. If you have multiple NumPy arrays in sigma1 then you can write all of these out to your file using writerows as follows:

with open('Data_sigma.csv', 'w') as f:
     writer = csv.writer(f)
     writer.writerows(sigma1)

Writing a list of NumPy arrays to csv

You can un-nest data with itertools.chain.from_iterable and use wr.writerow.

>>> from itertools import chain
>>> 
>>> with open("data.csv", mode='w') as csvfile:
...:      wr = csv.writer(csvfile, quoting=csv.QUOTE_ALL, dialect="excel")
...:      wr.writerow(chain.from_iterable(data))                                                                                                                 

Output:

$ cat data.csv
"178.0","76.0","184.0","92.0","164.0","90.0","154.0","116.0","160.0","126.0","204.0","94.0","208.0","124.0","190.0","132.0","164.0","152.0"

Export numpy array in a for loop into one CSV in Python

with open("output.csv", "a") as f:   # use 'a' instead of 'ab'
    np.savetxt(f, img_binary,  fmt="%d", delimiter=",")
    f.write("\n")

You should open your file in append mode. Or by default savetxt() rewrites the file everytime.

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