plm (version 1.5-12)

index.plm: Extract the indexes of panel data

Description

This function extracts the information about the structure of the individual and time dimensions of panel data.

Usage

"index"(x, which = NULL, ...)
"index"(x, which = NULL, ...)
"index"(x, which = NULL, ...)
"index"(x, which = NULL, ...)

Arguments

x

an object of class "pindex", "pdata.frame", "pseries" or "panelmodel",

which

the index(es) to be extracted (see details),

...

further arguments.

Value

a vector or a "data.frame" containing either one or both indexes.

Details

panel data are stored in a "pdata.frame" which has an "index" attribute. Fitted models in "plm" has a "model" element which is also a "pdata.frame" and therefore also have an "index" attribute. Finally, each series in a "pdata.frame" is of class "pseries", which also have this "index" attribute. "index" methods are available for all these objects. The argument "which" indicates which index should be extracted. If NULL, both indexes are extracted, but "which" can also be a vector of lenght 1 or 2 containing either characters (the names of the individual and of the time periods or "id" and "time") or integers (1 for the individual index and 2 for the time index.)

See Also

plm

Examples

data("Grunfeld", package = "plm")
Gr <- pdata.frame(Grunfeld, index = c("firm", "year"))
m <- plm(inv ~ value + capital, data = Gr)
index(Gr, "firm")
index(Gr, "time")
index(Gr$inv, c(2, 1))
index(m, "id")