to_matrix function

Build a Matrix from Measure and ID Variables

Build a matrix where the elements are values of a measure variable, and the rows and columns are formed by observed combinations of ID variables. The ID variables picked out by rows and cols must uniquely identify cells. to_matrix(), unlike stats::xtabs(), does not sum across multiple combinations of ID variables.

to_matrix(x, rows, cols, measure)

Arguments

• x: A data frame.
• rows: The ID variable(s) used to distinguish rows in the matrix.
• cols: The ID variable(s) used to distinguish columns in the matrix.
• measure: The measure variable, eg rates or counts.

Returns

A matrix

Examples

x <- expand.grid(age = c(0, 1, 2),
                 sex = c("F", "M"),
                 region = c("A", "B"),
                 year = 2000:2001)
x$count <- 1:24

to_matrix(x,
          rows = c(age, sex),
          cols = c(region, year),
          measure = count)

to_matrix(x,
          rows = c(age, sex, region),
          cols = year,
          measure = count)

## cells not uniquely identified
try(
to_matrix(x,
          rows = age,
          cols = sex,
          measure = count)
)