plm (version 2.6-4)

pdata.frame: pdata.frame: a data.frame for panel data

Description

An object of class 'pdata.frame' is a data.frame with an index attribute that describes its individual and time dimensions.

Usage

pdata.frame(
  x,
  index = NULL,
  drop.index = FALSE,
  row.names = TRUE,
  stringsAsFactors = FALSE,
  replace.non.finite = FALSE,
  drop.NA.series = FALSE,
  drop.const.series = FALSE,
  drop.unused.levels = FALSE,
  ...
)
# S3 method for pdata.frame
$(x, name) <- value
# S3 method for pdata.frame
[(x, i, j, drop)
# S3 method for pdata.frame
[[(x, y)
# S3 method for pdata.frame
$(x, y)
# S3 method for pdata.frame
print(x, ...)
# S3 method for pdata.frame
as.list(x, keep.attributes = FALSE, ...)
# S3 method for pdata.frame
as.data.frame(
  x,
  row.names = NULL,
  optional = FALSE,
  keep.attributes = TRUE,
  ...
)

Value

a pdata.frame object: this is a data.frame with an index attribute which is a data.frame with two variables, the individual and the time indexes, both being factors. The resulting pdata.frame is sorted by the individual index, then by the time index.

Arguments

x

a data.frame for the pdata.frame function and a pdata.frame for the methods,

index

this argument indicates the individual and time indexes. See Details,

drop.index

logical, indicates whether the indexes are to be excluded from the resulting pdata.frame,

row.names

NULL or logical, indicates whether "fancy" row names (combination of individual index and time index) are to be added to the returned (p)data.frame (NULL and FALSE have the same meaning for pdata.frame; for as.data.frame.pdata.frame see Details),

stringsAsFactors

logical, indicating whether character vectors are to be converted to factors,

replace.non.finite

logical, indicating whether values for which is.finite() yields TRUE are to be replaced by NA values, except for character variables (defaults to FALSE),

drop.NA.series

logical, indicating whether all-NA columns are to be removed from the pdata.frame (defaults to FALSE),

drop.const.series

logical, indicating whether constant columns are to be removed from the pdata.frame (defaults to FALSE),

drop.unused.levels

logical, indicating whether unused levels of factors are to be dropped (defaults to FALSE) (unused levels are always dropped from variables serving to construct the index variables),

...

further arguments passed on to internal usage of data.frame.

name

the name of the data.frame,

value

the name of the variable to include,

i

see Extract(),

j

see Extract(),

drop

see Extract(),

y

one of the columns of the data.frame,

keep.attributes

logical, only for as.list and as.data.frame methods, indicating whether the elements of the returned list/columns of the data.frame should have the pdata.frame's attributes added (default: FALSE for as.list, TRUE for as.data.frame),

optional

see as.data.frame(),

Author

Yves Croissant

Details

The index argument indicates the dimensions of the panel. It can be:

• a vector of two character strings which contains the names of the individual and of the time indexes,

• a character string which is the name of the individual index variable. In this case, the time index is created automatically and a new variable called "time" is added, assuming consecutive and ascending time periods in the order of the original data,

• an integer, the number of individuals. In this case, the data need to be a balanced panel and be organized as a stacked time series (successive blocks of individuals, each block being a time series for the respective individual) assuming consecutive and ascending time periods in the order of the original data. Two new variables are added: "id" and "time" which contain the individual and the time indexes.

The "[[" and "$" extract a series from the pdata.frame. The "index" attribute is then added to the series and a class attribute "pseries" is added. The "[" method behaves as for data.frame, except that the extraction is also applied to the index attribute. A safe way to extract the index attribute is to use the function index() for 'pdata.frames' (and other objects).

as.data.frame removes the index attribute from the pdata.frame and adds it to each column. For its argument row.names set to FALSE row names are an integer series, TRUE gives "fancy" row names; if a character (with length of the resulting data frame), the row names will be the character's elements.

as.list behaves by default identical to base::as.list.data.frame() which means it drops the attributes specific to a pdata.frame; if a list of pseries is wanted, the attribute keep.attributes can to be set to TRUE. This also makes lapply work as expected on a pdata.frame (see also Examples).

See Also

index() to extract the index variables from a 'pdata.frame' (and other objects), pdim() to check the dimensions of a 'pdata.frame' (and other objects), pvar() to check for each variable if it varies cross-sectionally and over time. To check if the time periods are consecutive per individual, see is.pconsecutive().

Examples

# Gasoline contains two variables which are individual and time
# indexes
data("Gasoline", package = "plm")
Gas <- pdata.frame(Gasoline, index = c("country", "year"), drop.index = TRUE)

# Hedonic is an unbalanced panel, townid is the individual index
data("Hedonic", package = "plm")
Hed <- pdata.frame(Hedonic, index = "townid", row.names = FALSE)

# In case of balanced panel, it is sufficient to give number of
# individuals data set 'Wages' is organized as a stacked time
# series
data("Wages", package = "plm")
Wag <- pdata.frame(Wages, 595)

# lapply on a pdata.frame by making it a list of pseries first
lapply(as.list(Wag[ , c("ed", "lwage")], keep.attributes = TRUE), lag)