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# NumPy | fromfunction method

schedule Aug 12, 2023
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Numpy's fromfunction(~) method constructs a Numpy array using a function that initializes the value for each cell.

# Parameters

1. functionlink | callable

A function that takes in row and column indexes, and returns a value for that cell.

2. shape | sequence of int

A desired shape of the resulting array.

3. dtype | string or type | optional

The desired data type of the resulting array. By default, dtype=Float.

A Numpy array.

# Examples

## Using an anonymous function

To create a 2 by 2 Numpy array with the diagonals set as True and elsewhere as False:

np.fromfunction(lambda i,j: i==j, (2,2))
array([[ True, False],
[False, True]])

Here, the function takes in as argument the row and column indexes.

## Using an explicit function

Here, we are defining an explicit function called foo:

def foo(i, j):
return i + j

We can use the fromfunction(~) method like so:

np.fromfunction(foo, (3,3))
array([[0., 1., 2.],
[1., 2., 3.],
[2., 3., 4.]])
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