# NumPy concatenate() function

In this tutorial, we will cover the `concatenate()` function of the NumPy library.

The `concatenate()` function is mainly used in order to combine two or more NumPy arrays together. ence we can say that the `concatenate()` function can be used to join a sequence of arrays along an existing axis.

• With the help of this function you can concatenate arrays together either horizontally or vertically.

• Concatenation of two numpy arrays simply means their stacking.

• This function joins two or more arrays having same shape and along the specified axis.

### Syntax of `numpy.concatenate()`:

The syntax required to use this function is as follows:

``numpy.concatenate((a1, a2, ...), axis=0, out=None)``

Parameters:

Let us take a look at the parameters of this function:

• (a1, a2 , ...)
This parameter indicates the sequence of array like structures or arrays. Here `a1`, `a2`, ... are the arrays having the same shape, which are to be concatenated together.

• axis
This parameter is used to define the axis along which the array will be concatenated. The default value of this parameter is 0.

• out
It is an optional parameter, which if provided then it simply indicates the destination where the result will be placed. If no `out` argument is specified then the shape must be correct, and should match with that of what concatenate would have returned.

Returned Values:

The `concatenate()` function will return the concatenated array as a result.

## Example 1: With axis=0

Let us have a look at the basic example of this function and the code snippet for the same is as follows:

``````import numpy as np

array1 = np.array([[5, 4], [6, 8]])
print("First Array is:\n",array1)
array2 = np.array([[13, 5], [72, 9]])
print("Second Array is :\n",array2)
out= np.concatenate((array1, array2), axis = 0)
print("The result of concatenation is :")
print (out)
`````` ## Example 2: With Axis=1

Below we have another example where we will take axis=1:

``````import numpy as np

array1 = np.array([[5, 4], [6, 8]])
print("First Array is:\n",array1)
array2 = np.array([[13, 5], [72, 9]])
print("Second Array is :\n",array2)
out= np.concatenate((array1, array2), axis = 1)
print("The result of concatenation is :")
print (out) `````` ## Summary

This tutorial was all about `concatenate()` function in the Numpy library. We haave covered how it is used with its syntax, its parameters and values returned by this function.