NumPy strings.ljust()

The numpy.strings.ljust() function left-justifies each string element in an array within a specified width. If the string is shorter than the specified width, it is padded with spaces or a specified fill character.

Syntax

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numpy.strings.ljust(a, width, fillchar=' ')

Parameters

Parameter	Type	Description
`a`	array-like (StringDType, bytes_, or str_)	Array of strings to be left-justified.
`width`	array_like (integer dtype)	The total length of each resulting string after justification.
`fillchar`	array-like (StringDType, bytes_, or str_), optional	The character used for padding (default is space).

Return Value

Returns an ndarray of strings, bytes, or StringDType, depending on the input type. Each string is left-justified to the specified width.

Examples

1. Left-Justifying Strings with Spaces

In this example, we left-justify an array of fruit names to a width of 10 characters using the default space character.

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import numpy as np

# Define an array of fruit names
fruits = np.array(["apple", "banana", "cherry"], dtype="U10")

# Left-justify with a width of 10 using spaces (default)
result = np.strings.ljust(fruits, 10)

# Print the results
print("Left-justified strings with spaces:")
print(result)

Output:

Left-justified strings with spaces:
['apple     ' 'banana    ' 'cherry    ']

Each string is padded with spaces on the right to make its length equal to 10.

2. Left-Justifying Strings with a Custom Fill Character

Here, we use the '-' character instead of spaces for padding.

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import numpy as np

# Define an array of fruit names
fruits = np.array(["apple", "banana", "cherry"], dtype="U10")

# Left-justify with a width of 10 using a custom fill character '-'
result = np.strings.ljust(fruits, 10, fillchar='-')

# Print the results
print("Left-justified strings with '-' as fill character:")
print(result)

Output:

['apple-----' 'banana----' 'cherry----']

Each string is now padded with '-' instead of spaces.

3. Using Different Widths for Each String

We specify different widths for each string to justify them dynamically.

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import numpy as np

# Define an array of fruit names
fruits = np.array(["apple", "banana", "cherry"], dtype="U10")

# Define different widths for each string
widths = np.array([8, 12, 15])

# Left-justify strings with different widths
result = np.strings.ljust(fruits, widths)

# Print the results
print("Left-justified strings with varying widths:")
print(result)

Output:

Left-justified strings with varying widths:
['apple   ' 'banana      ' 'cherry         ']

Each string is left-justified according to its corresponding width value.

4. Left-Justifying Byte Strings

We justify byte strings instead of Unicode strings.

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import numpy as np

# Define an array of fruit names as byte strings
fruits = np.array([b"apple", b"banana", b"cherry"], dtype="S10")

# Left-justify with a width of 10 using spaces
result = np.strings.ljust(fruits, 10)

# Print the results
print("Left-justified byte strings with spaces:")
print(result)

Output:

Left-justified byte strings with spaces:
[b'apple     ' b'banana    ' b'cherry    ']

Byte strings are also left-justified using the specified width.

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NumPy strings.ljust() – Left Justify Strings in Array