NumPy String: numpy.char.chararray() function

Last update on March 29 2023 09:21:33 (UTC/GMT +8 hours)

numpy.char.chararray() function

The numpy.char.chararray() is a class that represents a flexible array of strings. It is used to create arrays of strings of a fixed length. The chararray class provides a set of string operations that can be applied element-wise to each string in the array.

Versus a regular NumPy array of type str or unicode, this class adds the following functionality:

values automatically have whitespace removed from the end when indexed.
comparison operators automatically remove whitespace from the end when comparing values.
vectorized string operations are provided as methods (e.g. endswith) and infix operators (e.g. "+", "*", "%").

Syntax:

numpy.char.chararray(shape, itemsize=1, unicode=False, buffer=None, offset=0, strides=None, order=None)

Parameters:

Name	Description	Required / Optional
shape: tuple	Shape of the array.	Required
itemsize: int	Length of each array element, in number of characters. Default is 1.	Optional
unicode: bool	Are the array elements of type unicode (True) or string (False). Default is False.	Optional
buffer: bool	Memory address of the start of the array data. Default is None, in which case a new array is created.	Optional
offset: int	Fixed stride displacement from the beginning of an axis? Default is 0. Needs to be >=0.	Optional
strides: array_like of ints	Strides for the array (see ndarray.strides for full description). Default is None.	Optional
order: {‘C’, ‘F’}	The order in which the array data is stored in memory: 'C' -> “row major” order (the default), 'F' -> “column major” (Fortran) order.	Optional

Return value:

Example: Creating a chararray and assigning a value

>>> import numpy as np
>>> charary = np.chararray((4, 5))
>>> charary[:] = 'x'
>>> charary
chararray([[b'x', b'x', b'x', b'x', b'x'],
       [b'x', b'x', b'x', b'x', b'x'],
       [b'x', b'x', b'x', b'x', b'x'],
       [b'x', b'x', b'x', b'x', b'x']], 
      dtype='|S1')

The above code creates a chararray of shape (4, 5) with the numpy function np.chararray(). Here, the data type is set to '|S1', which means a one-byte string. Then, the [:] operator is used to assign the value 'x' to all the elements of the array. The resulting charary array is a 2-dimensional array of bytes, where each element is the string 'x'.

Example: Creating a chararray and assigning values to it

>> import numpy as np
>>> charary = np.chararray((4, 5))
>>> charary = np.chararray(charary.shape, itemsize=7)
>>> charary[:] = 'abc' 
>>> print(charary)
[[b'abc' b'abc' b'abc' b'abc' b'abc']
 [b'abc' b'abc' b'abc' b'abc' b'abc']
 [b'abc' b'abc' b'abc' b'abc' b'abc']
 [b'abc' b'abc' b'abc' b'abc' b'abc']]

In the given code, a numpy chararray object is created with dimensions (4,5) using the np.chararray() method. The shape of the array is (4,5), which means it has 4 rows and 5 columns. The [:] is used to assign a value of 'x' to all the elements of the chararray.

After that, the chararray is recreated with the same dimensions but with a specified item size of 7 using the np.chararray() method.

The [:] operator is then used to assign a string 'abc' to each element of the chararray. Finally, the resulting chararray is printed.

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