Add one row to another

Write a NumPy program to add row 2 to row 1.

[[6, 5], [10, 9], [7, 8]]

[[16 14]
 [10  9]
 [ 7  8]]

Approach

1. a[0] += a[1].

Solution

import numpy as npa = np.array([[6, 5], [10, 9], [7, 8]])a[0] += a[1]print(a)

[[16 14]
 [10  9]
 [ 7  8]]

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Multiply a row by a scalar

Write a NumPy program to multiply row 1 of an array by 2.

[[6, 5], [10, 9], [7, 8]]

[[12 10]
 [10  9]
 [ 7  8]]

Approach

1. Index the row and use *=.

Solution

import numpy as npa = np.array([[6, 5], [10, 9], [7, 8]])a[0] *= 2print(a)

[[12 10]
 [10  9]
 [ 7  8]]

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Reverse the row order

Write a NumPy program to swap the rows of an array (first and last).

[[6, 5], [10, 9], [7, 8]]

[[ 7  8]
 [10  9]
 [ 6  5]]

Approach

1. Fancy indexing with a new row order.

Solution

import numpy as npa = np.array([[6, 5], [10, 9], [7, 8]])a[[0, 2]] = a[[2, 0]]print(a)

[[ 7  8]
 [10  9]
 [ 6  5]]

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Replace numbers at or above a value

Write a NumPy program to replace numbers greater than or equal to 8 with 0.

[[6, 5], [10, 9], [7, 8]]

[[6 5]
 [0 0]
 [7 0]]

Approach

1. np.where(condition, new, old).

Solution

import numpy as npa = np.array([[6, 5], [10, 9], [7, 8]])print(np.where(a >= 8, 0, a))

[[6 5]
 [0 0]
 [7 0]]

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Numbers greater than a value

Write a NumPy program to extract numbers greater than 6.

[[6, 5], [10, 9], [7, 8]]

[10  9  7  8]

Approach

1. A boolean mask.

Solution

import numpy as npa = np.array([[6, 5], [10, 9], [7, 8]])print(a[a > 6])

[10  9  7  8]

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Sort rows by the first column

Write a NumPy program to sort the rows of an array by the first column.

[[6, 5], [10, 9], [7, 8]]

[[ 6  5]
 [ 7  8]
 [10  9]]

Approach

1. argsort on the column gives the row order.

Solution

import numpy as npa = np.array([[6, 5], [10, 9], [7, 8]])print(a[a[:, 0].argsort()])

[[ 6  5]
 [ 7  8]
 [10  9]]

Line by line

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Sort each row

Write a NumPy program to sort each row in ascending order.

[[6, 5], [10, 9], [8, 7]]

[[ 5  6]
 [ 9 10]
 [ 7  8]]

Approach

1. np.sort(a, axis=1).

Solution

import numpy as npprint(np.sort(np.array([[6, 5], [10, 9], [8, 7]]), axis=1))

[[ 5  6]
 [ 9 10]
 [ 7  8]]

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Transpose a matrix

Write a NumPy program to swap the rows and columns of a matrix.

[[5, 6], [7, 8], [9, 10]]

[[ 5  7  9]
 [ 6  8 10]]

Approach

1. .T.

Solution

import numpy as npprint(np.array([[5, 6], [7, 8], [9, 10]]).T)

[[ 5  7  9]
 [ 6  8 10]]

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One-dimensional array

Write a NumPy program to create a one-dimensional array.

[65 90  1  3  5] 1

Approach

1. np.array with a flat list.

Solution

import numpy as npa = np.array([65, 90, 1, 3, 5])print(a, a.ndim)

[65 90  1  3  5] 1

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Element-wise equality

Write a NumPy program to check whether two arrays are equal element-wise.

[5, 3], [7, 8]

[False False]

Approach

1. np.equal.

Solution

import numpy as npprint(np.equal([5, 3], [7, 8]))

[False False]

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