Understanding sort Function with index.return=TRUE in R: A Clear Guide

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The Problem

Consider the following vector in R:

[[See Video to Reveal this Text or Code Snippet]]

Suppose you attempt to sort this vector while also wanting to know the original positions of each element in the sorted list by using the command:

[[See Video to Reveal this Text or Code Snippet]]

The function will produce output that reveals the sorted vector ($x) and a corresponding index ($ix):

[[See Video to Reveal this Text or Code Snippet]]

Your first question might be, "What does this output mean, especially the $ix portion?" This confusion arises from what $ix represents.

Understanding the Output

$x vs $ix

$x: This is the sorted vector. It displays the values of vector A in ascending order.

$ix: This shows the indices of the original vector A that match the sorted values in $x.

In other words, $ix indicates where each value in the sorted array came from in the original array, rather than the reverse as one might expect.

Key Insights

Indexing Confusion: The first element of sorted $x is 0.3245712, which is the third element of the original vector A. Therefore, $ix[1] is 3, not 4. This means the smallest value's original position in A is 3.

Finding Maximum Values: The largest number in vector A is 63.2337407, which sits in the sixth position of A. In sorted $x, this value appears last, leading to $ix[8] being 6, not 8, as you might expect.

How to Get the Original Indices in Sorted Order

If you want the original positions back in an ordered form, there’s a simple method to achieve that:

[[See Video to Reveal this Text or Code Snippet]]

This command essentially rearranges the original indices according to the sorted sequence, allowing for a clearer understanding of where each sorted value is derived from.

Conclusion

Now that you have a clearer comprehension of how the sort function operates in R, feel free to explore further and apply these techniques in your data sorting tasks!