# Learn NumPy for Data Science (Course II)

July 19, 2020 2020-07-27 6:00## Learn NumPy for Data Science (Course II)

### Input-Output operations in NumPy

NumPy provides built-in functions for efficiently saving NumPy arrays as external files in the disk and also for loading the NumPy array from a file into your Python code. In this chapter, you will learn various ways of performing I/O operations in NumPy.

#### NPY and NPZ files in NumPy

Generally, the arrays are saved in files with the format `.npy`

and .`npz`

. The `.npy`

files store all the information required to reconstruct an array on any computer, which includes dtype and shape information whereas, several arrays are contained into a single file in uncompressed `.npz`

format.

The numpy.save() function is used to save the array in `.npy`

format, whereas numpy.savez() is used to save the array in `.npz`

format. Likewise, the numpy.load() function is used to load the array into the Python code. While loading the .npz file, the individual array can be accessed by passing “arr_0, arr_1, ….. arr_n”, a as a key to the loaded object.

import numpy as np # Creating two 1-D numpy arrays a = np.arange(start=1, stop=5, step=1) b = np.arange(start=6, stop=10, step=1) # Printing the arrays print("a: ", a) print("b: ", b) print("\n") # Saving the a to .npy format np.save('a.npy', a) # Saving the arrays a and b to .npz format np.savez('ab.npz', a, b) # Loading saved data a_loaded = np.load('a.npy') ab_loaded = np.load('ab.npz') # Printing the loaded data print("a_loaded: ", a_loaded) print("First array in the ab_loaded: ", ab_loaded['arr_0']) print("Second array in the ab_loaded: ", ab_loaded['arr_1'])

a: [1 2 3 4] b: [6 7 8 9] a_loaded: [1 2 3 4] First array in the ab_loaded: [1 2 3 4] Second array in the ab_loaded: [6 7 8 9]

#### TXT Files in NumPy

NumPy arrays can also be stored in plain `.txt`

file formats. The numpy.savetxt() and numpy.loadtxt() methods are used to save and load arrays respectively.

import numpy as np # Creating a 1-D numpy arrays a = np.arange(start=1, stop=5, step=1) # Saving array as a txt file np.savetxt("a.txt", a) # Loading array from txt file loaded_arr = np.loadtxt("a.txt") print("Loaded Array: ", loaded_arr)

Loaded Array: [1. 2. 3. 4.]

This is how you can perform Input-Output operations in NumPy!