This function extracts the information about the structure of the individual and time dimensions of panel data. Grouping information can also be extracted if the panel data were created with a grouping variable.
## S3 method for class 'pindex' index(x, which = NULL, ...) ## S3 method for class 'pdata.frame' index(x, which = NULL, ...) ## S3 method for class 'pseries' index(x, which = NULL, ...) ## S3 method for class 'panelmodel' index(x, which = NULL, ...)
an object of class
the index(es) to be extracted (see details),
Panel data are stored in a
"pdata.frame" which has an
attribute. Fitted models in
"plm" have a
"model" element which
is also a
"pdata.frame" and therefore also has an
attribute. Finally, each series, once extracted from a
"pdata.frame", becomes of class
"pseries", which also has this
"index" methods are available for all these
objects. The argument
"which" indicates which index should be
which = NULL, all indexes are extracted.
can also be a vector of length 1, 2, or 3 (3 only if the pdata
frame was constructed with an additional group index) containing
either characters (the names of the individual variable and/or of
the time variable and/or the group variable or
"group" or integers (1 for the individual index, 2 for the
time index, and 3 for the group index (the latter only if the pdata
frame was constructed with such).)
A vector or an object of class
containing either one index, individual and time index, or (any
combination of) individual, time and group indexes.
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") # with additional group index data("Produc", package = "plm") pProduc <- pdata.frame(Produc, index = c("state", "year", "region")) index(pProduc, 3) index(pProduc, "region") index(pProduc, "group")
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