Indexing in NumPy
This lesson will help you learn indexing in NumPy.
We'll cover the following...
We'll cover the following...
Indexing means to refer to any value in an array. Each item in a numpy array is stored at a specific index. To access value at a specific index write:
Z=np.arrange(9)
Z[0] #get the value at index 0
Get the First Value
To get the first value of a matrix, write: Z[0,0].
┏━━━┓───┬───┐ ┏━━━┓
┃ 0 ┃ 1 │ 2 │ → ┃ 0 ┃ (scalar)
┗━━━┛───┼───┤ ┗━━━┛
Z │ 3 │ 4 │ 5 │
├───┼───┼───┤
│ 6 │ 7 │ 8 │
└───┴───┴───┘
Python 3.5
import numpy as npZ = np.arange(9).reshape(3,3)print(Z[0,0])
Get the Last Value
To get the last value of a matrix, write: Z[-1,-1].
┌───┬───┬───┐
│ 0 │ 1 │ 2 │
├───┼───┼───┤
Z │ 3 │ 4 │ 5 │
├───┼───┏━━━┓ ┏━━━┓
│ 6 │ 7 ┃ 8 ┃ → ┃ 8 ┃ (scalar)
└───┴───┗━━━┛ ┗━━━┛
Python 3.5
import numpy as npZ = np.arange(9).reshape(3,3)print(Z[-1,-1])
Get a row from a Grid
To get a row from a grid, write: Z[row_index].
To get the first row from a grid, write: Z[1].
┌───┬───┬───┐
│ 0 │ 1 │ 2 │
┏━━━┳━━━┳━━━┓ ┏━━━┳━━━┳━━━┓
Z ┃ 3 ┃ 4 ┃ 5 ┃ → ┃ 3 ┃ 4 ┃ 5 ┃
┗━━━┻━━━┻━━━┛ ┗━━━┻━━━┻━━━┛
│ 6 │ 7 │ 8 │ (view)
└───┴───┴───┘
Python 3.5
import numpy as npZ = np.arange(9).reshape(3,3)print(Z[1])
Get a Column from a Grid
To get the column from a grid, use
Z[:,column_index]
To get the second column from a grid, use ...