znajdzPliki<-function(dir,ext,by="size",recursive=TRUE)
{
   stopifnot((by=="size"|by=="time"),is.logical(recursive),
             is.character(dir),is.character(ext),length(dir)==1,
             length(recursive)==1,length(ext)>0,
             length(list.files(dir))>0)
  n<-length(ext)
  x<-list.files(dir,
                pattern=stri_paste("\\.",
                           stri_paste(ext[-n],"|",collapse=""),ext[n],"$")
                ,recursive=recursive)

  x1<-file.path(dir,x)
  y<-file.info(x1)[c(1,5)]
  y1<-data.frame(sicezka_wzgledna=x,size=y$size,time=y$ctime)

  y2<-y1[order(y1[,by],decreasing =("size"==by)),]
  rownames(y2)=1:nrow(y2)
  y2

}