Github user felixcheung commented on a diff in the pull request:
https://github.com/apache/spark/pull/9613#discussion_r44735202
--- Diff: R/pkg/R/DataFrame.R ---
@@ -2200,4 +2200,107 @@ setMethod("coltypes",
rTypes[naIndices] <- types[naIndices]
rTypes
- })
\ No newline at end of file
+ })
+
+#' Display the structure of a DataFrame, including column names, column
types, as well as a
+#' a small sample of rows.
+#' @name str
+#' @title Compactly display the structure of a dataset
+#' @rdname str_data_frame
+#' @family dataframe_funcs
+#' @param x a DataFrame
+#' @examples \dontrun{
+#'
+#' # Create a DataFrame from the Iris dataset
+#' irisDF <- createDataFrame(sqlContext, iris)
+#'
+#' # Show the structure of the DataFrame
+#' str(irisDF)
+#'
+#' }
+setMethod("str", signature="DataFrame", definition=
+ function(object) {
+
+ # A synonym for easily concatenating strings
+ "%++%" <- function(x, y) {
+ paste(x, y, sep = "")
+ }
+
+ # TODO: These could be made global parameters, though in R
it's not the case
+ DEFAULT_HEAD_ROWS <- 6
+ MAX_CHAR_PER_ROW <- 120
+ MAX_COLS <- 100
+
+ # Get the column names and types of the DataFrame
+ names <- names(object)
+ types <- coltypes(object)
+
+ # Get the number of rows.
+ # TODO: Ideally, this should be cached
+ cachedCount <- nrow(object)
+
+ # Get the first elements of the dataset. Limit number of
columns accordingly
+ dataFrame <- if (ncol(object) > MAX_COLS) {
+ head(object[, c(1:MAX_COLS)],
DEFAULT_HEAD_ROWS)
+ } else {
+ head(object, DEFAULT_HEAD_ROWS)
+ }
+
+ # The number of observations will be displayed only if the
number
+ # of rows of the dataset has already been cached.
+ if (!is.null(cachedCount)) {
+ cat("'" %++% class(object) %++% "': " %++% cachedCount
%++% " obs. of " %++%
+ length(names) %++% " variables:\n")
+ } else {
+ cat("'" %++% class(object) %++% "': " %++% length(names)
%++% " variables:\n")
+ }
+
+ # Whether the ... should be printed at the end of each row
+ ellipsis <- FALSE
+
+ # Add ellipsis (i.e., "...") if there are more rows than
shown
+ if (!is.null(cachedCount)) {
+ if (nrow(object) > DEFAULT_HEAD_ROWS) {
+ ellipsis <- TRUE
+ }
+ }
+
+ if (nrow(dataFrame) > 0) {
+ for (i in 1 : ncol(dataFrame)) {
+ firstElements <- ""
+
+ # Get the first elements for each column
+ if (types[i] == "chr") {
+ firstElements <- paste("\"" %++% dataFrame[,i] %++%
"\"", collapse = " ")
+ } else {
+ firstElements <- paste(dataFrame[,i], collapse = " ")
+ }
+
+ # Add the corresponding number of spaces for alignment
+ spaces <- paste(rep(" ", max(nchar(names) -
nchar(names[i]))), collapse="")
+
+ # Get the short type. For 'character', it would be 'chr';
+ # 'for numeric', it's 'num', etc.
+ dataType <- SHORT_TYPES[[types[i]]]
+ if (is.null(dataType)) {
+ dataType <- substring(types[i], 1, 3)
+ }
+
+ # Concatenate the colnames, coltypes, and first
+ # elements of each column
+ line <- " $ " %++% names[i] %++% spaces %++% ": " %++%
+ dataType %++% " " %++% firstElements
+
+ # Chop off extra characters if this is too long
+ cat(substr(line, 1, MAX_CHAR_PER_ROW))
--- End diff --
do we need to chop off extra to fit in 4 char in " ..."?
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