<p>In <a href="https://github.com/mlpack/mlpack/pull/694#discussion_r70190073">src/mlpack/core/data/imputation_methods/listwise_deletion.hpp</a>:</p>
<pre style='color:#555'>&gt; +              const T&amp; mappedValue,
&gt; +              const size_t dimension,
&gt; +              const bool transpose = true)
&gt; +  {
&gt; +    // initiate output
&gt; +    output = input;
&gt; +    size_t count = 0;
&gt; +
&gt; +    if (transpose)
&gt; +    {
&gt; +      for (size_t i = 0; i &lt; input.n_cols; ++i)
&gt; +      {
&gt; +         if (input(dimension, i) == mappedValue ||
&gt; +             std::isnan(input(dimension, i)))
&gt; +         {
&gt; +           output.shed_col(i - count);
</pre>
<p>I tested listwise_deletion to impute iris.csv with 100000 looping.<br>
Original Way<br>
[INFO ]   impute: 4.265383s<br>
Cols() Way<br>
[INFO ]   impute: 4.129703s<br>
Turns out that using cols() is slightly faster.</p>

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