How to concatenate string vectors of unequal length?

John Michell answered . 2025-03-23 03:03:35

To concatenate string vectors of unequal lengths into a single matrix in MATLAB, you can use padding to ensure all vectors have the same number of elements. Here’s how you can achieve this:

Solution

You can achieve the desired result by:

1. Determining the maximum length of the input vectors.
2. Padding shorter vectors with empty strings ('') to match the maximum length.
3. Concatenating the vectors into a matrix.

Code Example:

% Input vectors
v1 = {'a'; 'b'; 'c'};
v2 = {'d'};
v3 = {'e'; 'f'};

% Combine the vectors into a cell array
vectors = {v1, v2, v3};

% Find the maximum length of the vectors
max_length = max(cellfun(@numel, vectors));

% Pad each vector with empty strings to match the maximum length
padded_vectors = cellfun(@(v) [v; repmat({''}, max_length - numel(v), 1)], ...
                         vectors, 'UniformOutput', false);

% Concatenate the padded vectors horizontally
v4 = [padded_vectors{:}];

% Display the result
disp(v4);

Output

The result will be:

    'a'    'd'    'e'
    'b'    ''     'f'
    'c'    ''     ''

Explanation

1. Find Maximum Length: Use cellfun with @numel to determine the number of elements in each vector and get the maximum.
2. Pad with Empty Strings: For each vector, append enough empty strings ('') to make its length equal to the maximum.
3. Concatenate Horizontally: Use horizontal concatenation ([ ... ]) to combine the padded vectors.

This approach works for any number of input vectors and handles variable lengths seamlessly.

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