commonItems: Identify Common Items for Several Groups
In eatTools: eatTools

Description Usage Arguments Details Value Author(s) See Also Examples

This function identifies sets of items that have been administered to two groups of persons.

1	commonItems(dat, group.var, na = NA, uncommon = FALSE, simplify = TRUE)

`dat`	A data frame with item responses and a grouping variable.
`group.var`	Name or column number of the group variable in `dat`
`na`	A character string indicating which value should be considered as not administered (missing by design)
`uncommon`	if `TRUE` a vector of items that have only been administered to one of the two groups is additionally returned.
`simplify`	if `TRUE` a character vector is returned (only in case of 2 groups and `uncommon=FALSE`)

dat must only contain the group variable and the items, if further variables are in dat they are treated as items. If group.var specifies more than two groups, pairwise group comparisons are performed.

returns a list of all group.var combinations with character vectors of common item names. If uncommon=TRUE a vector of uncommon (unique) items of each group is additionally returned.

The names of list elements are the two group names concatenated by "|".

Martin Hecht

commonItems.percent

data(science1)
d <- science1[ , c("version", science1.items)]

# common items are listed for each combination of groups
str(commonItems(dat = d, group.var = "version", na = "mbd"))

# uncommon items are returned as well
str(commonItems(dat = d, group.var = "version", na = "mbd", uncommon = TRUE))