Below is a version of [.data.frame that is faster
for subscripting rows of large data frames; it avoids calling
duplicated(rows)
if there is no need to check for duplicate row names, when:
i is logical
attr(x, "dup.row.names") is not NULL (S+ compatibility)
i is numeric and negative
i is strictly increasing
"[.data.frame" <-
function (x, i, j,
drop = if (missing(i)) TRUE else length(cols) == 1)
{
# This version of [.data.frame avoid wasting time enforcing unique
# row names.
mdrop <- missing(drop)
Narg <- nargs() - (!mdrop)
if (Narg < 3) {
if (!mdrop)
warning("drop argument will be ignored")
if (missing(i))
return(x)
if (is.matrix(i))
return(as.matrix(x)[i])
y <- NextMethod("[")
cols <- names(y)
if (!is.null(cols) && any(is.na(cols)))
stop("undefined columns selected")
if (any(duplicated(cols)))
names(y) <- make.unique(cols)
return(structure(y, class = oldClass(x),
row.names = .row_names_info(x, 0L)))
}
if (missing(i)) {
if (missing(j) && drop && length(x) == 1L)
return(.subset2(x, 1L))
y <- if (missing(j))
x
else .subset(x, j)
if (drop && length(y) == 1L)
return(.subset2(y, 1L))
cols <- names(y)
if (any(is.na(cols)))
stop("undefined columns selected")
if (any(duplicated(cols)))
names(y) <- make.unique(cols)
nrow <- .row_names_info(x, 2L)
if (drop && !mdrop && nrow == 1L)
return(structure(y, class = NULL, row.names = NULL))
else return(structure(y, class = oldClass(x),
row.names = .row_names_info(x, 0L)))
}
xx <- x
cols <- names(xx)
x <- vector("list", length(x))
x <- .Call("R_copyDFattr", xx, x, PACKAGE = "base")
oldClass(x) <- attr(x, "row.names") <- NULL
# Do not want to check for duplicates if don't need to
noDuplicateRowNames <- (is.logical(i) ||
(!is.null(attr(x, "dup.row.names"))) ||
(is.numeric(i) && min(i, 0, na.rm=TRUE) < 0) ||
(!notSorted(i, strict = TRUE)))
if (!missing(j)) {
x <- x[j]
cols <- names(x)
if (drop && length(x) == 1L) {
if (is.character(i)) {
rows <- attr(xx, "row.names")
i <- pmatch(i, rows, duplicates.ok = TRUE)
}
xj <- .subset2(.subset(xx, j), 1L)
return(if (length(dim(xj)) != 2L) xj[i] else xj[i,
, drop = FALSE])
}
if (any(is.na(cols)))
stop("undefined columns selected")
nxx <- structure(seq_along(xx), names = names(xx))
sxx <- match(nxx[j], seq_along(xx))
}
else sxx <- seq_along(x)
rows <- NULL
if (is.character(i)) {
rows <- attr(xx, "row.names")
i <- pmatch(i, rows, duplicates.ok = TRUE)
}
for (j in seq_along(x)) {
xj <- xx[[sxx[j]]]
x[[j]] <- if (length(dim(xj)) != 2L)
xj[i]
else xj[i, , drop = FALSE]
}
if (drop) {
n <- length(x)
if (n == 1L)
return(x[[1L]])
if (n > 1L) {
xj <- x[[1L]]
nrow <- if (length(dim(xj)) == 2L)
dim(xj)[1L]
else length(xj)
drop <- !mdrop && nrow == 1L
}
else drop <- FALSE
}
if (!drop) {
if (is.null(rows))
rows <- attr(xx, "row.names")
rows <- rows[i]
if ((ina <- any(is.na(rows))) | (dup <- !noDuplicateRowNames &&
any(duplicated(rows)))) {
if (ina)
rows[is.na(rows)] <- "NA"
if (dup)
rows <- make.unique(as.character(rows))
}
if (any(duplicated(nm <- names(x))))
names(x) <- make.unique(nm)
if (is.null(rows))
rows <- attr(xx, "row.names")[i]
attr(x, "row.names") <- rows
oldClass(x) <- oldClass(xx)
}
x
}
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