R: Pad Matrix-Like Objects with a Value

pad {collapse}

R Documentation

Pad Matrix-Like Objects with a Value

Description

The pad function inserts elements / rows filled with value into a vector matrix or data frame X at positions given by i. It is particularly useful to expand objects returned by statistical procedures which remove missing values to the original data dimensions.

Usage

pad(X, i, value = NA, method = c("auto", "xpos", "vpos"))

Arguments

X

a vector, matrix, data frame or list of equal-length columns.

i

either an integer (positive or negative) or logical vector giving positions / rows of X into which value's should be inserted, or, alternatively, a positive integer vector with length(i) == NROW(X), but with some gaps in the indices into which value's can be inserted, or a logical vector with sum(i) == NROW(X) such that value's can be inserted for FALSE values in the logical vector. See also method and Examples.

value

a scalar value to be replicated and inserted into X at positions / rows given by i. Default is NA.

method

an integer or string specifying what the use of i. The options are:

Int.	String	Description
1	"auto"	automatic method selection: If `i` is positive integer and `length(i) == NROW(X)` or if `i` is logical and `sum(i) == NROW(X)`, choose method "xpos", else choose "vpos".


1	"xpos"	`i` is a vector of positive integers or a logical vector giving the positions of the the elements / rows of `X`. `values`'s are inserted where there are gaps / `FALSE` values in `i`.


2	"vpos"	`i` is a vector of positive / negative integers or a logical vector giving the positions at which `values`'s / rows should be inserted into `X`.

Value

X with elements / rows filled with value inserted at positions given by i.

Examples

v <- 1:3

pad(v, 1:2)       # Automatic selection of method "vpos"
pad(v, -(1:2))    # Same thing
pad(v, c(TRUE, TRUE, FALSE, FALSE, FALSE)) # Same thing

pad(v, c(1, 3:4)) # Automatic selection of method "xpos"
pad(v, c(TRUE, FALSE, TRUE, TRUE, FALSE))  # Same thing

head(pad(wlddev, 1:3)) # Insert 3 missing rows at the beginning of the data
head(pad(wlddev, 2:4)) # ... at rows positions 2-4

# pad() is mostly useful for statistical models which only use the complete cases:
mod <- lm(LIFEEX ~ PCGDP, wlddev)
# Generating a residual column in the original data (automatic selection of method "vpos")
settfm(wlddev, resid = pad(resid(mod), mod$na.action))
# Another way to do it:
r <- resid(mod)
i <- as.integer(names(r))
resid2 <- pad(r, i)        # automatic selection of method "xpos"
# here we need to add some elements as flast(i) < nrow(wlddev)
resid2 <- c(resid2, rep(NA, nrow(wlddev)-length(resid2)))
# See that these are identical:
identical(unattrib(wlddev$resid), resid2)

# Can also easily get a model matrix at the dimensions of the original data
mm <- pad(model.matrix(mod), mod$na.action)