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NumPy | putmask method

schedule Aug 11, 2023

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Parameters Return value Examples Basic usage 2D arrays Setting a single value Setting multiple values

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Numpy's putmask(~) sets a specific value in the input array given a boolean mask. This is done in-place, that is, no new Numpy array is created.

Parameters

1. a | array-like

The input array. All arrays are treated as a flattened array.

2. mask | array-like of booleans

An array of booleans that indicate whether or not to set the value. The shape must be the same as that of a.

3. values | array-like

The values to set. If v is shorter than a, then v will be repeated to ensure the shape matches up.

Return value

None - the setting is done in-place.

Examples

Basic usage


        
        
            
                
                
                    a = np.array([5,6,7,8])
np.putmask(a, [True, False, True, False], 9)
a
                
            
            array([9, 6, 9, 8])

Notice how only values that had a corresponding value of True in the mask were set.

2D arrays

Consider the following 2D array:


        
        
            
                
                
                    a = np.array([[5,6],[7,8]])
a
                
            
            array([[5, 6],
       [7, 8]])

Setting a single value


        
        
            
                
                
                    np.putmask(a, [True, False, True, False], 9)
a
                
            
            array([[9, 6],
       [9, 8]])

All arrays are treated as a flattened array.

Setting multiple values


        
        
            
                
                
                    a = np.array([[5,6],[7,8]])
np.putmask(a, [True, True, False, False], [9,10])
a
                
            
            array([[ 9, 10],
       [ 7,  8]])

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Published by Isshin Inada

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