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# NumPy | take method

schedule Aug 10, 2023
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Numpy's take(~) method is used to access values, rows and columns of an array.

# Parameters

1. a | array_like

The array to perform the method on.

2. indices | number or array_like

The indices of the values to be fetched. If you provide a number type, then you're accessing a single value, row or column in the array. If array_like type is provided, then you're accessing multiple rows/columns.

3. axis | number | optional

The axis along which to select values. By default, axis=None, that is, your input array a will be deemed as a flattened array.

# Return value

Depending on the parameters, the return type will differ.

• If no axis is provided, then you get a number since you're just accessing a single value.

• If axis is provided, then you get a Numpy array since you're accessing a row or a column.

# Examples

## Accessing a single value in a matrix

 x = [[4,5,6], [7,8,9]]np.take(x, 1) 5 

Remember, if you provide a number type for the second argument, then Numpy will treat your input array as a flattened array, that is, x=[4,5,6,7,8,9]. In this example, we're taking the first index of this flattened array, and so the value 5 is returned.

## Accessing a single row of a matrix

To access a row of a matrix, supply the parameter axis=0.

 x = [[4,5,6], [7,8,9]]np.take(x, 1, axis=0) array([7, 8, 9]) 

To clarify what this code is doing, we're just fetching the 2nd row (i.e. rows also follow index order, so that's why we set 1 as the second argument):

$$\begin{pmatrix} 4&5&6\\ \color{red}{7}&\color{red}{8}&\color{red}{9}\\ \end{pmatrix}$$

## Accessing a single column of a matrix

To access a column of a matrix, supply the parameter axis=1.

 x = [[4,5,6], [7,8,9]]np.take(x, 1, axis=1) array([5, 8]) 

To clarify what this code is doing, we're just fetching the 2nd column (i.e. columns also follow index order, so that's why we set 1 as the second argument):

$$\begin{pmatrix} 4&\color{red}{5}&6\\ 7&\color{red}{8}&9\\ \end{pmatrix}$$

## Accessing multiple rows of a matrix

To access multiple columns of a matrix, supply the parameter axis=0, and provide type array-like for the second argument:

 x = [[4,5,6], [7,8,9]]np.take(x, [0,1], axis=0) array([[4, 5, 6], [7, 8, 9]]) 

We're accessing 1st and 2nd rows, as in:

$$\begin{pmatrix} \color{red}{4}&\color{red}{5}&\color{red}{6}\\ \color{red}{7}&\color{red}{8}&\color{red}{9}\\ \end{pmatrix}$$

## Accessing multiple columns of a matrix

To access multiple columns of a matrix, supply the parameter axis=1, and provide type array-like for the second argument:

 x = [[4,5,6], [7,8,9]]np.take(x, [0,2], axis=1) array([[4, 6], [7, 9]]) 

We're accessing the 1st and 3rd columns, as in:

$$\begin{pmatrix} \color{red}{4}&5&\color{red}{6}\\ \color{red}{7}&8&\color{red}{9}\\ \end{pmatrix}$$
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