Sorting

Sorting is a fundamental component of data analysis. Basic sorting is trivial: just calling sort! will sort all columns, in place:

using DataFrames, RDatasets

iris = dataset("datasets", "iris")
sort!(iris)

In Sorting DataFrames, you may want to sort different columns with different options. Here are some examples showing most of the possible options:

sort!(iris, rev = true)
sort!(iris, cols = [:SepalWidth, :SepalLength])

sort!(iris, cols = [order(:Species, by = uppercase),
                    order(:SepalLength, rev = true)])

Keywords used above include cols (to specify columns), rev (to sort a column or the whole DataFrame in reverse), and by (to apply a function to a column/DataFrame). Each keyword can either be a single value, or can be a tuple or array, with values corresponding to individual columns.

As an alternative to using array or tuple values, order to specify an ordering for a particular column within a set of columns

The following two examples show two ways to sort the iris dataset with the same result: Species will be ordered in reverse lexicographic order, and within species, rows will be sorted by increasing sepal length and width:

sort!(iris, cols = (:Species, :SepalLength, :SepalWidth),
      rev = (true, false, false))

sort!(iris, cols = (order(:Species, rev = true), :SepalLength, :SepalWidth))