devel/movedToNMdata/findVars.R

In philipdelff/pmxtricks: Every-day pharmacometrics helper functions

##' Extract columns that vary within values of other columns in a data.frame
##'
##' @param data data.frame in which to look for covariates
##' @param cols.id optional covariates will be searched for in
##'     combinations of values in these columns. Often cols.id will be
##'     either empty or ID. But it can also be both say c("ID","DRUG")
##'     or c("ID","TRT").
##' @param debug start by running browser()?
##' @family DataWrangling
##' @import data.table


findVars <- function(data,cols.id=NULL,debug=F){
    if(debug) browser()
    ## check arguments
    if(!is.data.frame(data)){
        stop("data must be a data.frame (or data.table)")
    }
    
    was.data.table <- T
    if(!is.data.table(data)){
        was.data.table <- F
        data <- as.data.table(data)
    }

    ## The way this is done below requires a by column to exist. So if
    ## by is NULL, we make a constant dummy.
    rm.tmp <- FALSE
    if(is.null(cols.id)){
        cols.id <- tmpcol(data)
        data[,(cols.id):=1]
        rm.tmp <- TRUE
    }
    
    ## uniqueN > 1
    dt2 <- data[, .SD[, lapply(.SD, function(x)uniqueN(x)>1)], by=cols.id]
    ## use any
    ifkeep <- dt2[,sapply(.SD,any),.SDcols=!(cols.id)]
    keep <- c(cols.id,setdiff(colnames(dt2),cols.id)[ifkeep])
    reduced <- unique(data[,keep,with=F])

    if(rm.tmp) reduced[,(cols.id):=NULL]
    if(!was.data.table) reduced <- as.data.frame(reduced)
    reduced

}