Group-mean centering.

Compute group-mean centered variables. Usually used for HLM level-1 predictors.

Usage

group_mean_center(
  data,
  vars = setdiff(names(data), by),
  by,
  std = FALSE,
  add.suffix = "",
  add.group.mean = "_mean"
)

Arguments

data

Data object.

vars

Variable(s) to be centered.

by

Grouping variable.

std

Standardized or not. Defaults to FALSE.

add.suffix

The suffix of the centered variable(s). Defaults to "". You may set it to "_c", "_center", etc.

add.group.mean

The suffix of the variable name(s) of group means. Defaults to "_mean" (see Examples).

Value

A new data object containing the centered variable(s).

See also

grand_mean_center

Examples

d = data.table(x=1:9, g=rep(1:3, each=3))

d.c = group_mean_center(d, "x", by="g")
d.c
#>        x     g x_mean
#>    <num> <int>  <num>
#> 1:    -1     1      2
#> 2:     0     1      2
#> 3:     1     1      2
#> 4:    -1     2      5
#> 5:     0     2      5
#> 6:     1     2      5
#> 7:    -1     3      8
#> 8:     0     3      8
#> 9:     1     3      8

d.c = group_mean_center(d, "x", by="g", add.suffix="_c")
d.c
#>        x     g x_mean   x_c
#>    <int> <int>  <num> <num>
#> 1:     1     1      2    -1
#> 2:     2     1      2     0
#> 3:     3     1      2     1
#> 4:     4     2      5    -1
#> 5:     5     2      5     0
#> 6:     6     2      5     1
#> 7:     7     3      8    -1
#> 8:     8     3      8     0
#> 9:     9     3      8     1