Data Frames

A data frame is R's table — rows and columns, with each column holding its own type — and it's the structure almost all of R's data-analysis tools are built around.

Building a data frame

students <- data.frame(
  name = c("Ava", "Sam", "Lee"),
  score = c(88, 92, 79)
)
students

  name score
1  Ava    88
2  Sam    92
3  Lee    79

data.frame() takes one or more equal-length vectors and lines them up as columns, automatically numbering the rows down the left side.

Accessing a column with $

students$score
mean(students$score)

[1] 88 92 79
[1] 86.33333

students$score pulls out the score column as a plain vector, which is why you can hand it straight to mean().

Basic indexing with [row, column]

students[1, ]
students[, "name"]

  name score
1  Ava    88
[1] "Ava" "Sam" "Lee"

students[1, ] leaves the column position blank, meaning "every column" for row 1. students[, "name"] does the reverse — every row, just the name column.