Python – Mapping Matrix with Dictionary

When working with matrices (lists of lists) in Python, you often need to map numerical values to meaningful strings using a dictionary. This technique is useful for converting coded data into readable format.

Basic Matrix Mapping

Here's how to map matrix elements using a dictionary with nested loops ?

my_matrix = [[2, 4, 3], [4, 1, 3], [2, 1, 3, 4]]

print("Original matrix:")
print(my_matrix)

# Mapping dictionary
map_dict = {2: "Python", 1: "fun", 3: "to", 4: "learn"}

# Map matrix elements
result = []
for row in my_matrix:
    mapped_row = []
    for element in row:
        mapped_row.append(map_dict[element])
    result.append(mapped_row)

print("Mapped matrix:")
print(result)

Original matrix:
[[2, 4, 3], [4, 1, 3], [2, 1, 3, 4]]
Mapped matrix:
[['Python', 'learn', 'to'], ['learn', 'fun', 'to'], ['Python', 'fun', 'to', 'learn']]

Using List Comprehension

A more concise approach using nested list comprehension ?

my_matrix = [[2, 4, 3], [4, 1, 3], [2, 1, 3, 4]]
map_dict = {2: "Python", 1: "fun", 3: "to", 4: "learn"}

# One-liner mapping
result = [[map_dict[element] for element in row] for row in my_matrix]

print("Original matrix:")
print(my_matrix)
print("Mapped matrix:")
print(result)

Original matrix:
[[2, 4, 3], [4, 1, 3], [2, 1, 3, 4]]
Mapped matrix:
[['Python', 'learn', 'to'], ['learn', 'fun', 'to'], ['Python', 'fun', 'to', 'learn']]

Handling Missing Keys

Use get() method to handle keys that might not exist in the dictionary ?

my_matrix = [[2, 4, 5], [1, 3, 6]]  # 5 and 6 not in dictionary
map_dict = {2: "Python", 1: "fun", 3: "to", 4: "learn"}

# Safe mapping with default values
result = [[map_dict.get(element, "unknown") for element in row] for row in my_matrix]

print("Matrix with unmapped values:")
print(my_matrix)
print("Safely mapped matrix:")
print(result)

Matrix with unmapped values:
[[2, 4, 5], [1, 3, 6]]
Safely mapped matrix:
[['Python', 'learn', 'unknown'], ['fun', 'to', 'unknown']]

Comparison

Conclusion

Matrix mapping with dictionaries transforms numerical data into meaningful strings. Use nested loops for clarity, list comprehension for conciseness, or get() method for safer mapping with default values.