Create check_for_seq.r

R/check_for_seq.r

@@ -0,0 +1,81 @@
+## This file contains 
+##   check_for_seq()  and  convert_to_col_number_and_check_valid()
+## for allowing  .SDcols='b':'d'  and/or  by='g':'k'
+##
+## Todo:  Test against  unquoted column names
+##        can NOT yet handle nested functions,
+##           such as  c('b':'d')  or  do.call(paste, list("V", c(3, 7)))
+
+
+
+check_for_seq <- function(input, x) {
+## If input is of the form
+##      from:to
+## this function will interpret from and to to reference columns
+## from, to can be integers or column names
+## they do NOT need to be of the same type
+##
+## If the input is NOT of the above form, the input is returned unchanged
+##
+
+  arg <- as.list(substitute(input))
+
+  ## if input is not of the expected form, return it unchanged
+  if (!(arg[[1]] == ':' & length(arg) == 3)) 
+    return(input)
+
+  from <- convert_to_col_number_and_check_valid ( arg[[2]], x, showWarnings=TRUE )
+  to   <- convert_to_col_number_and_check_valid ( arg[[3]], x, showWarnings=TRUE )
+
+  return( names(x)[from:to] )
+
+}
+
+
+convert_to_col_number_and_check_valid <- function(cn, x, showWarnings=TRUE) {
+## returns the column number of x corresponding to cn
+## while performing several checks to ensure validity
+##
+## cn : a column name or column number
+##      if it is numeric, then we simply check to ensure it is within seq(x)
+##      if it is factor,  it is coerced to character with optional warning
+##      otherwise, it is presumed a character and any coercian will be done by `==`
+##                 in the line  which(cn == names(x))
+
+
+  ## x must have valid names
+  if (is.null(names(x)))
+    stop ("x must have valid names. They are names(x) is NULL")
+
+  ## if input is.name, we need to deparse it
+  if (is.name(cn))
+    cn <- deparse(cn)
+
+  ## factors are too ambiguous. Do we interpret the character value 
+  if (is.factor(cn)) {
+    if (isTRUE(showWarnings))
+      warning("input is a factor and will be coerced to character")
+    cn <- as.character(cn)
+  }
+
+  ## match to col index number
+  if (is.numeric(cn))
+    col <- cn
+  else 
+    col <- which(cn == names(x))
+
+
+  ## ERROR CHECK: confirm there is one and exactly one match
+  ## --------------- ##
+    extra_error_msg <- "\n\nNOTE: using 'b':'d' is a new feature.\nIf you feel this is error should not have occured, please report it."
+
+    if (! length(col))  ## No Match
+      stop ("'", cn, "' is not a name of a column of the data.table.", extra_error_msg)
+    if (length(col) > 1)  ## More than one match
+      stop ("'", cn, "' matches more than one (", length(col), ") columns of the data.table.\nConsider using make.names()", extra_error_msg)
+    if (!any(col == seq(x))) ## outside range of x
+      stop ("'", cn, "' is byeond the range of the seq(x) which is from (1:", length(x), ").", extra_error_msg)
+  ## --------------- ##
+
+  return(col)
+}