NumPy strings.upper() – Convert Array to Uppercase

NumPy strings.upper()

The numpy.strings.upper() function converts each string element in an input array to uppercase, applying the Python str.upper() method element-wise.

Syntax

numpy.strings.upper(a)

Parameters

Parameter	Type	Description
a	array-like	Input array containing string elements. Can have StringDType, bytes_, or str_ dtype.

Return Value

Returns an array with the same shape as the input, where all string elements have been converted to uppercase.

---

Examples

1. Converting a Single String to Uppercase

Here, we convert a single string to uppercase using NumPy.

import numpy as np

# Define a single string as a NumPy array
word = np.array("apple", dtype="U")

# Convert to uppercase
result = np.strings.upper(word)

# Print the result
print("Uppercase string:", result)

Output:

Uppercase string: APPLE

2. Converting an Array of Strings to Uppercase

We apply numpy.strings.upper() to an array of multiple words.

import numpy as np

# Define an array of strings
words = np.array(["apple", "banana", "cherry"], dtype="U")

# Convert each element to uppercase
uppercase_words = np.strings.upper(words)

# Print the result
print("Original words:", words)
print("Uppercase words:", uppercase_words)

Output:

Original words: ['apple' 'banana' 'cherry']
Uppercase words: ['APPLE' 'BANANA' 'CHERRY']

3. Using Uppercase Conversion with Byte Strings

NumPy also allows the conversion of byte strings to uppercase.

import numpy as np

# Define an array of byte strings
byte_words = np.array([b"grape", b"mango"], dtype="S")

# Convert byte strings to uppercase
uppercase_byte_words = np.strings.upper(byte_words)

# Print the result
print("Original byte words:", byte_words)
print("Uppercase byte words:", uppercase_byte_words)

Output:

Original byte words: [b'grape' b'mango']
Uppercase byte words: [b'GRAPE' b'MANGO']

4. Converting Strings in a Structured NumPy Array

Using numpy.strings.upper() on a structured array with string fields.

import numpy as np

# Define a structured array with string fields
dtype = [("fruit", "U10"), ("color", "U10")]
data = np.array([("apple", "red"), ("banana", "yellow")], dtype=dtype)

# Convert only the 'fruit' field to uppercase
data["fruit"] = np.strings.upper(data["fruit"])

# Print the result
print("Structured array with uppercase fruits:")
print(data)

Output:

Structured array with uppercase fruits:
[('APPLE', 'red') ('BANANA', 'yellow')]

Only the fruit field is modified, while the color field remains unchanged.