In This Article You Will Learn About Python Numpy Slicing.
Python Numpy Slicing – Before moving ahead, let’s know a little bit about Python Numpy Indexing.
Slicing in arrays
Slice in Python means to move elements from one index to another.
We use slice instead of the index as follows: [start: end].
It is also defined as the step by using this format: [start end; step].
If we fail to pass start, it is considered 0
If it doesn’t pass the end its length is the array’s dimension.
If we fail to pass step, it is considered 1
Example – Slicing the elements from index 2 to index 6 from the array.
import numpy as np Array = np.array([1, 2, 3, 4, 5, 6, 7]) print(Array[2:6])
Output - [3 4 5 6]
Note: It includes the starting index number, but excludes the ending index number.
Example – Slicing elements from index 2 to the ending element of the array.
import numpy as np Array = np.array([1, 2, 3, 4, 5, 6, 7]) print(Array[2:])
Output - [3 4 5 6 7]
Example – Slicing elements from beginning to index number 5.
import numpy as np Array = np.array([1, 2, 3, 4, 5, 6, 7]) print(Array[:6])
Output - [1 2 3 4 5 6]
Negative Slicing
Use the minus operator to define an index from the ending point.
Example – Slicing from the index 4 from the end to index 2 from the end:
import numpy as np Array = np.array([1, 2, 3, 4, 5, 6, 7]) print(Array[-4:-2])
Output - [4 5]
STEP
To determine the step value of the slicing, use the step value:
Example – Returning every 2nd element from index 1 to index 7.
import numpy as np Array = np.array([1, 2, 3, 4, 5, 6, 7]) print(Array[1:7:2])
Output - [2 4 6]
Example – Returning every 2nd element from the whole array.
import numpy as np Array = np.array([1, 2, 3, 4, 5, 6, 7]) print(Array[::2])
Output - [1 3 5 7]
Slicing 2-D Arrays
Example – From the second element, slicing elements from index 1 to index 4.
import numpy as np Array = np.array([[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]]) print(Array[1, 1:4])
Output - [7 8 9]
Note: Last index number is excluded.
Example – Returning index number 1’s element from an array.
import numpy as np Array = np.array([[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]]) print(Array[0:2, 1])
Output - [2 7]
Example – From the arrays, slice index 0 to index 3 (not included), this will return a 2-D array:
import numpy as np Array = np.array([[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]]) print(Array[0:3, 0:3])
As a result, it returned an array containing from index 0 to index 3 (not included).
If you find anything incorrect in the above-discussed topic and have any further questions, please comment below.
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