NumPy arrays can be saved and loaded using different file formats. Examples of using the NumPy file formats .npy and .npz as well as a plain text format are given below.
Using the npy format
Use the NumPy save() function to save an array to a .npy file. Use the load() function to load the array from the file.
import numpy as np
# Save an array named `z` to an `.npy` file
z = np.array([[3, 4, 8.91], [1.05, 2, 7], [5.4, 3, 1]])
with open('zarray.npy', 'wb') as file:
np.save(file, z)
# Load the array data from the `.npy` file into `zz`
with open('zarray.npy', 'rb') as file:
zz = np.load(file)
# Print results
print('z is\n', z)
print('zz is\n', zz)
Output from the above example is shown below.
z is
[[3. 4. 8.91]
[1.05 2. 7. ]
[5.4 3. 1. ]]
zz is
[[3. 4. 8.91]
[1.05 2. 7. ]
[5.4 3. 1. ]]
Using the npz format
Use the savez() function to save several arrays to a single .npz file. Use the load() function to load the saved arrays from the file.
import numpy as np
# Save arrays `a`, `b`, `c` to an `.npz` file
a = np.array([[4, 5, 81], [10, 2, 7], [1, 21, 5]])
b = np.array([[90, 51, 81], [10, 21, 74], [19, 1, 15]])
c = np.array([[0.1, 5.8, 0.71], [3.9, 2, 7.9], [1.05, 21, 5]])
with open('zdata.npz', 'wb') as file:
np.savez(file, a=a, b=b, c=c)
# Load arrays `aa`, `bb`, `cc` from the `.npz` file
with np.load('zdata.npz') as data:
aa = data['a']
bb = data['b']
cc = data['c']
# Print results
print('a is\n', a)
print('b is\n', b)
print('c is\n', c)
print('aa is\n', aa)
print('bb is\n', bb)
print('cc is\n', cc)
Output from this example is given below.
a is
[[ 4 5 81]
[10 2 7]
[ 1 21 5]]
b is
[[90 51 81]
[10 21 74]
[19 1 15]]
c is
[[ 0.1 5.8 0.71]
[ 3.9 2. 7.9 ]
[ 1.05 21. 5. ]]
aa is
[[ 4 5 81]
[10 2 7]
[ 1 21 5]]
bb is
[[90 51 81]
[10 21 74]
[19 1 15]]
cc is
[[ 0.1 5.8 0.71]
[ 3.9 2. 7.9 ]
[ 1.05 21. 5. ]]
Using plain text format
A plain text format can also be used to save and load a NumPy array with the savetxt() and loadtxt() functions.
import numpy as np
# Save array to a text file
a = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
np.savetxt('array.txt', a)
# Load array from a text file named `array.txt`
b = np.loadtxt('array.txt')
# Print comparison of `a` and `b`
print('a is\n', a)
print('b is\n', b)
