# Python – Rear elements Average in List

Sometimes, while working with data, we can have a problem in which we need to perform the mean of all the rear element that come after K. This can be an application in Mathematics and Data Science domain. Lets discuss certain ways in which this task can be performed.

Method #1 : Using `sum()` + list comprehension
The combination of above functionalities can be used to perform this task. In this, we first let the initial K element be as they are and perform sum of rest of element and divide by number of element left.

 `# Python3 code to demonstrate  ` `# Rear elements Average in List ` `# using list comprehension + sum() ` ` `  `# Initializing list ` `test_list ``=` `[``5``, ``6``, ``4``, ``7``, ``8``, ``1``, ``10``] ` ` `  `# printing original list ` `print``(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# Initializing K  ` `K ``=` `3` ` `  `# Rear elements Average in List ` `# using list comprehension + sum() ` `res ``=` `test_list[ : K] ``+` `[``sum``(test_list[K:]) ``/` `len``(test_list[K: ])] ` ` `  `# printing result  ` `print` `(``"Average List after K elements : "` `+` `str``(res)) `

Output :

```The original list is : [5, 6, 4, 7, 8, 1, 10]
Average List after K elements : [5, 6, 4, 6.5]
```

Method #2 : Using `mean()` + list comprehension
This is yet another way in which this task can be performed. In this, we perform the task of finding mean using mean(), rest of task is same as above method.

 `# Python3 code to demonstrate  ` `# Rear elements Average in List ` `# using list comprehension + mean() ` `from` `statistics ``import` `mean ` ` `  `# Initializing list ` `test_list ``=` `[``5``, ``6``, ``4``, ``7``, ``8``, ``1``, ``10``] ` ` `  `# printing original list ` `print``(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# Initializing K  ` `K ``=` `3` ` `  `# Rear elements Average in List ` `# using list comprehension + mean() ` `res ``=` `[``*``test_list[:K], mean(test_list[K:])] ` ` `  `# printing result  ` `print` `(``"Average List after K elements : "` `+` `str``(res)) `

Output :

```The original list is : [5, 6, 4, 7, 8, 1, 10]
Average List after K elements : [5, 6, 4, 6.5]
```

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