Skip to contents

Split Data into Groups (Extended Interface)

Source: R/splitX.R
splitX.Rd

Splits a vector or object into groups defined by a factor or grouping variables. This is a wrapper around split() with an additional formula interface.

Usage

splitX(x, ...)

# Default S3 method
splitX(x, f, drop = FALSE, ...)

# S3 method for class 'formula'
splitX(formula, data, subset, na.action, drop = FALSE, ...)

Arguments

x

object to be split (typically a vector).

...

further arguments passed to split().

f

a factor or list of factors defining the groups (default method).

drop

logical; if TRUE, unused factor levels are dropped.

formula

a formula of the form y ~ group or y ~ g1 + g2 specifying the variable to split (y) and the grouping variables.

data

a data frame containing the variables in the formula.

subset

optional logical expression indicating rows to include.

na.action

a function specifying how missing values are handled, passed to model.frame() (e.g., na.omit()).

Value

a list of subsets of x, grouped according to f or the grouping variables in the formula.

Details

splitX extends split() by providing:

  • an S3 interface

  • a formula method for convenient specification of variables

  • support for multiple grouping variables via formula

The formula interface evaluates a model.frame() and splits the response variable by one or more grouping variables.

If multiple grouping variables are provided, the data are split by their interaction (similar to split(..., interaction(...))).

See also

Other data.reshape: collapseTable(), long-wide-reshape, splitAt(), untable()

Examples

# Default usage
x <- 1:10
g <- rep(letters[1:2], each = 5)
splitX(x, g)
#> $a
#> [1] 1 2 3 4 5
#> 
#> $b
#> [1]  6  7  8  9 10
#> 

# Formula interface
df <- data.frame(
  y = rnorm(10),
  g1 = rep(letters[1:2], each = 5),
  g2 = rep(1:2, times = 5)
)

splitX(y ~ g1, data = df)
#> $a
#> [1]  0.5350384 -0.5836362 -2.1614605 -1.3202132  0.8104089
#> 
#> $b
#> [1]  1.3416652  0.6925525 -0.3231760 -0.1173097 -0.4226757
#> 
#> attr(,"data.name")
#> [1] "y by g1 (rows)"
splitX(y ~ g1 + g2, data = df)
#> $a.1
#> [1]  0.5350384 -2.1614605  0.8104089
#> 
#> $b.1
#> [1]  0.6925525 -0.1173097
#> 
#> $a.2
#> [1] -0.5836362 -1.3202132
#> 
#> $b.2
#> [1]  1.3416652 -0.3231760 -0.4226757
#> 
#> attr(,"data.name")
#> [1] "y by g1 : g2 (rows)"