Unzip rows back into columns

A table comes back from the server as rows. Your chart wants columns: all the x values in one array, all the y values in another. That is a transpose.

Implement unzip(rows) where rows is an array of arrays. Return an array of columns: column j contains the element at index j from each row, in row order. The result has as many columns as the longest row. Where a shorter row has no element at that index, use null. An empty rows array returns an empty array. Applying unzip twice to a rectangular input gives back the original structure.

What it has to do

• Produce one column per index of the longest row.
• Keep values in row order within each column.
• Fill gaps from shorter rows with null.
• Return [] for an empty input.
• Round-trip correctly: unzipping a rectangular result twice returns the original.

Your workspace