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% File src/library/base/man/drop.Rd
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% File src/library/base/man/drop.Rd
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% Part of the R package, https://www.R-project.org
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2021 R Core Team
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% Copyright 1995-2024 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{drop}
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\name{drop}
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\alias{drop}
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\alias{drop}
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\title{Drop Redundant Extent Information}
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\title{Drop Redundant Extent Information}
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If \code{x} is an object with a \code{dim} attribute (e.g., a matrix
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If \code{x} is an object with a \code{dim} attribute (e.g., a matrix
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or \code{\link{array}}), then \code{drop} returns an object like
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or \code{\link{array}}), then \code{drop} returns an object like
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\code{x}, but with any extents of length one removed. Any
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\code{x}, but with any extents of length one removed. Any
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accompanying \code{dimnames} attribute is adjusted and returned with
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accompanying \code{dimnames} attribute is adjusted and returned with
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\code{x}: if the result is a vector the \code{names} are taken from
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\code{x}: if the result is a vector the \code{names} are taken from
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the \code{dimnames} (if any). If the result is a length-one vector,
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the \code{dimnames} (if any). However, if the result is a vector
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the names are taken from the first dimension with a \I{dimname}.
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of length one, then it does not get \code{names} \emph{unless} exactly
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one component of the \code{dimnames} is non-\code{NULL}, in which case
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that component is used.
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Array subsetting (\code{\link{[}}) performs this reduction unless used
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Array subsetting (\code{\link{[}}) performs this reduction unless used
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with \code{drop = FALSE}, but sometimes it is useful to invoke
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with \code{drop = FALSE}, but sometimes it is useful to invoke
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\code{drop} directly.
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\code{drop} directly.
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}
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}
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\code{\link{drop1}} which is used for dropping terms in models, and
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\code{\link{drop1}} which is used for dropping terms in models, and
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\code{\link{droplevels}} used for dropping unused levels from a \code{\link{factor}}.
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\code{\link{droplevels}} used for dropping unused levels from a \code{\link{factor}}.
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}
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}
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\examples{
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\examples{
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dim(drop(array(1:12, dim = c(1,3,1,1,2,1,2)))) # = 3 2 2
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dim(drop(array(1:12, dim = c(1,3,1,1,2,1,2)))) # = 3 2 2
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drop(1:3 \%*\% 2:4) # scalar product
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drop(1:3 \%*\% 2:4) # scalar product - w/o drop(.), would return 1x1 matrix
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# Behavior when result is length-1 vector:
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(x <- x1 <- x2 <- array(0, c(1L, 1L), list("a", "b")))
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colnames(x1) <- rownames(x2) <- NULL
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names(drop(x )) # NULL
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names(drop(x1)) # "a"
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names(drop(x2)) # "b"
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}
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}
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\keyword{array}
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\keyword{array}
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