# np.diff: How to Find Difference Between Numbers in Array

The **np.diff()** is a **numpy** **array** function that **finds the difference **numbers in an array. The **np.diff()** function can be applied to a single array and multiple arrays. If a single array is passed then the difference is found by res[i] = arr[i+1] – arr[i].

**Syntax**

`numpy.diff(a, n = 1, axis= -1, prepend = < no value >, append = < no value >)`

**Arguments**

The **np.diff()** function takes five arguments as a parameter:

**a**: It is the array for which the difference is found using the**np.diff()**function.**n**: The number of times the array is differenced is passed as the argument to n. This is by default set to 1.**axis**: It is the axis in which the difference is calculated. It means that from right to left are from left to right. By default, the value is set to -1. However, we can also have the axis as 0.**prepend**: The values appended at the beginning before performing the**diff()**function.**append**: The values that are appended at the ending before performing the**diff()**function.

**Return value**

The np.diff() function returns an array. This array consists of values that are the difference between the two numbers in an array.

**Python program for finding the difference in a single array using np.diff()**

```
# Importing numpy as np
import numpy as np
# Creating an array arr
arr = np.array([5, 10, 7, 11, 15])
# creating a new array by using the diff function
diff_arr = np.diff(arr)
print(diff_arr)
```

**Output**

`[ 5 -3 4 4]`

In this program, we imported numpy library and created a numpy array using the **np.array()** function. Then, we passed this array into the **np.diff()** function. Hence, we passed the value for a. The function performs the operations like diff_arr[i] = arr[i+1] – arr[i].

Hence, the first index will store the difference between the first two elements, which is 10 – 5; therefore, the first element is 5. Then in the second index of the **diff_arr**, the value is stored as 7 – 10 is -3. Similarly, this function calculates for all the elements in the array.

**Program for finding the difference in multiple arrays inside the single array using the np.diff() function**

```
# Importing numpy as np
import numpy as np
# Creating an array arr
arr = np.array([[5, 10, 7, 11, 15], [5, 20, 5, 15, 10]])
# creating a new array by using the diff function
diff_arr = np.diff(arr, n=1, axis=0)
print(diff_arr)
```

**Output**

`[[ 0 10 -2 4 -5]]`

In this program, we performed the **np.diff()** function in axis 0. Hence, it does the difference function like subtracting the first array elements from the second array elements. The internal formula is: **diff_arr[0][i] = arr[1][i]-arr[0][i]**. Hence, the first element of the **diff_arr** is equal to 5 – 5 = 0. Similarly, the others are calculated.

That’s it for the **numpy diff()** function in **Python**.