2D indexing
Two numbers, row then column, select a single cell in a table.
In this page:
Syntax
arr[row, col]2D indexing
Use arr[row, col] to reach one element of a 2-D array. This comma form is faster and clearer than chained arr[row][col]. A single index such as arr[1] returns the whole row.
Note:
Both arr[1][2] and arr[1, 2] work, but the comma version does one lookup instead of two.
Example: 2D indexing
import numpy as np
m = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
print(m[1, 2])
print(m[0])
print(m[2][0])
# Output:
# 6
# [1 2 3]
# 7Related Topics
Common Mistakes
- Swapping row and column order
- Using chained indexing when assigning to slices
- Expecting arr[1] to return a single value
Chapter Summary
- Use arr[row, col]
- One index returns a whole row
- Rows come first then columns
- Comma indexing is preferred
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