Torch/Lua equivalent function to MATLAB or Numpy 'Unique'

Question

In Python one can do the following to get the unique values in a vector/matrix/tensor:

import numpy as np

a = np.unique([1, 1, 2, 2, 3, 3])
# Now a = array([1, 2, 3])

There is a similar function in MATLAB as well:

A = [9 2 9 5];
C = unique(A)
%Now C = [9, 2, 9]

Is there an equivalent function in Torch/Lua as well?

Answer 1

Nope, there is no such a standard function in stock Lua and/or Torch.

Considering using some implementation of set data structure, rolling Your own implementation of unique() or redesigning Your application not to require this kind of functionality.

Example 11-liner:

function vector_unique(input_table)
    local unique_elements = {} --tracking down all unique elements
    local output_table = {} --result table/vector

    for _, value in ipairs(input_table) do
        unique_elements[value] = true
    end

    for key, _ in pairs(unique_elements) do
        table.insert(output_table, key)
    end

    return output_table
end

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