Subsetting and Cleaning

Ordering Rows

Sorting by a Column

order returns row positions in sorted order. Data frames use those positions to rearrange rows.

Program

Play the script to rank rows by points and choose the winner.

ordering.R
Replay: real traced execution (multi-file project)
scores <- data.frame(name = c("Ada", "Lin", "Mia"), points = c(9, 12, 10))
ranked <- scores[order(scores$points, decreasing = TRUE), ]
winner <- ranked$name[1]
cat(winner, "\n", sep = "")

  1. scores ← 3 rows x 2 cols

    1scores <- data.frame(name = c("Ada", "Lin", "Mia"), points = c(9, 12, 10))2ranked <- scores[order(scores$points, decreasing = TRUE), ]
    values this step3 rows x 2 colsscores

  2. ranked ← 3 rows x 2 cols

    1scores <- data.frame(name = c("Ada", "Lin", "Mia"), points = c(9, 12, 10))2ranked <- scores[order(scores$points, decreasing = TRUE), ]3winner <- ranked$name[1]
    values this step3 rows x 2 colsranked3 rows x 2 colsscores

  3. winner ← Lin

    2ranked <- scores[order(scores$points, decreasing = TRUE), ]3winner <- ranked$name[1]4cat(winner, "\n", sep = "")
    values this stepLinwinnerLinranked$name[1]

  4. cat(winner, " ", sep = "")

    3winner <- ranked$name[1]4cat(winner, "\n", sep = "")
    outputLin
    values this stepLinwinner

Follow the Sort

  1. scores starts with Ada 9, Lin 12, and Mia 10.
  2. order(scores$points, decreasing = TRUE) ranks the highest points first.
  3. The row order becomes Lin, Mia, Ada.
  4. winner <- ranked$name[1] reads the first ranked name.
  5. The script prints Lin. | rank | name | points | | --- | --- | --- | | 1 | Lin | 12 | | 2 | Mia | 10 | | 3 | Ada | 9 |
order `order(scores$points)` returns row positions sorted by points.
decreasing `decreasing = TRUE` sorts highest values first.
row subset `scores[rows, ]` reorders the rows and keeps every column.

Exercise: ordering.R

Reproduce the printed winner Lin, then identify the sorted row order from highest points to lowest.