R/drop.r

In genvar: An Imperative Library for Data Manipulation

## This file is part of genvar.

## genvar is free software: you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation, under version 3 of the License.

## genvar is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.

## You should have received a copy of the GNU General Public License
## along with genvar.  If not, see <https://www.gnu.org/licenses/>.


#' drops rows from the dataset
#'
#' @param x a condition like \code{var1==2} describing the observations that should be removed from the data set.
#' @return returns NULL, invisibly
#' @examples
#' use(cars, clear=TRUE)
#' listif()
#' dropif(speed <= 20)
#' listif()
#'@export
dropif <- function (x)
{
  assert_loaded()
  x <- gvcharexpr(enquo(x))
  eval(substitute({
    rows <- with(data, which(eval(parse(text=x))))
    data <- data[-rows,]}), envir=data.env)
  postuse()
  invisible(NULL)
}

#' drops variables in varlist format from the dataset
#' @param x a varlist in "var1 var2 var3" format or unquoted if a single variable
#' @return returns NULL, invisibly
#' @examples
#' use(cars, clear=TRUE)
#' listif()
#' dropvar(speed)
#' listif()
#' @export
dropvar <- function (x)
{
  assert_loaded()
  x <- gvcharexpr(enquo(x))
  x <- structure_varlist(x, type="vector")
  eval(substitute({data[,x] <- NULL}),envir=data.env)
  postuse()
  invisible(NULL)
}

#' keeps some rows in the dataset and drops the rest
#'
#'
#' @param x a condition like: \code{var1==2} in which case observations that satisfy the condition are kept and all others are removed.
#' @return returns NULL, invisibly
#' @examples
#' use(cars, clear=TRUE)
#' keepif(speed <= 20)
#' listif()
#' @export
keepif <- function (x)
{
  assert_loaded()
  x <- gvcharexpr(enquo(x))
  rows <- eval(substitute(with(data, which(eval(parse(text=x))))),
               envir=data.env)
  eval(substitute({data <- data[rows,]}), envir=data.env)
  postuse()
  invisible(NULL)
}

#' keeps some variables in the dataset and drops the others
#'
#' @param x a varlist either of the form "var1 var2 var3" or, if a single variable, it can be unquoted.
#' @return returns NULL, invisibly
#' @examples
#' use(cars, clear=TRUE)
#' keepvar(speed)
#' listif()
#'@export
keepvar <- function (x)
{
  assert_loaded()
  x <- gvcharexpr(enquo(x))
  x <- structure_varlist(x, type="vector")

  eval(substitute({data <- as.data.frame(data[,x])}),envir=data.env)
  eval(substitute({names(data) <- x }),envir=data.env)
  postuse()
  invisible(NULL)
}