[R-gregmisc-users] SF.net SVN: r-gregmisc:[1978] trunk/gdata

[<wa...@us...>]

Revision: 1978
          http://sourceforge.net/p/r-gregmisc/code/1978
Author:   warnes
Date:     2015-04-28 04:44:08 +0000 (Tue, 28 Apr 2015)
Log Message:
-----------
- first() and last() are now simply wrappers to utils::head() and
  utils::tail() with a default 'n=1' instead of 'n=6'.
- Move code for left() and right() into a separate file.

Modified Paths:
--------------
    trunk/gdata/R/first.R
    trunk/gdata/man/first.Rd

Added Paths:
-----------
    trunk/gdata/R/left.R

Modified: trunk/gdata/R/first.R
===================================================================
--- trunk/gdata/R/first.R	2015-04-28 04:41:39 UTC (rev 1977)
+++ trunk/gdata/R/first.R	2015-04-28 04:44:08 UTC (rev 1978)
@@ -1,30 +1,3 @@
-first <- function(x) UseMethod("first")
-last  <- function(x) UseMethod("last")
-
-left  <- function(x, n=6) UseMethod("left")
-right <- function(x, n=6) UseMethod("left")
-
-
-first.default <- function(x) x[1]
-last.default  <- function(x) x[length(x)] 
-
-
-first.list <- function(x) x[[1]]
-last.list  <- function(x) x[[length(x)]]
-
-
-left.data.frame <- function(x, n=6)
-{
-   n <- min(n, ncol(x))
-   x[, 1:n]
-}
-left.matrix <- left.data.frame
-
-
-right.data.frame <- function(x, n=6)
-{
-   n <- min(n, ncol(x))
-   x[, (ncol(x)-n+1):ncol(x)]
-}
-right.matrix <- right.data.frame
-
+# Simply call 'first' or 'last' with a different default value for 'n'.
+first <- function(x, n=1, ...) head(x, n=n, ...)
+last  <- function(x, n=1, ...) tail(x, n=n, ...)

Added: trunk/gdata/R/left.R
===================================================================
--- trunk/gdata/R/left.R	                        (rev 0)
+++ trunk/gdata/R/left.R	2015-04-28 04:44:08 UTC (rev 1978)
@@ -0,0 +1,38 @@
+left  <- function(x, n=6L) UseMethod("left")
+right <- function(x, n=6L) UseMethod("left")
+
+left.data.frame <- function(x, n=6)
+{
+    stopifnot(length(n) == 1L)
+    n <- if (n < 0L)
+        max(ncol(x) + n, 0L)
+    else min(n, ncol(x))
+    x[, seq_len(n), drop = FALSE]
+}
+left.matrix <- left.data.frame
+
+
+right.data.frame <- function (x, n = 6L, ...)
+{
+    stopifnot(length(n) == 1L)
+    ncx <- ncol(x)
+    n <- if (n < 0L)
+        max(ncx + n, 0L)
+    else min(n, ncx)
+    x[, seq.int(to = ncx, length.out = n), drop = FALSE]
+}
+
+right.matrix <- function (x, n = 6L, addcolnums = TRUE, ...)
+{
+    stopifnot(length(n) == 1L)
+    ncx <- ncol(x)
+    n <- if (n < 0L)
+        max(ncx + n, 0L)
+    else min(n, ncx)
+    sel <- seq.int(to = ncx, length.out = n)
+    ans <- x[, sel, drop = FALSE]
+    if (addcolnums && is.null(colnames(x)))
+        colnames(ans) <- paste0("[", sel, ",]")
+    ans
+}
+

Modified: trunk/gdata/man/first.Rd
===================================================================
--- trunk/gdata/man/first.Rd	2015-04-28 04:41:39 UTC (rev 1977)
+++ trunk/gdata/man/first.Rd	2015-04-28 04:44:08 UTC (rev 1978)
@@ -1,28 +1,25 @@
 \name{first}
 \alias{first}
-\alias{first.default}
-\alias{first.list}
 \alias{last}
-\alias{last.default}
-\alias{last.list}
-\title{Return first or last element of a vector or list}
+\title{Return first or last element of an object}
 \description{
-  Return first or last element of a vector or list
-}
+  Return first or last element of an object.  These functions are convenience
+  wrappers for \code{head(x, n=1, ...)} and \code{tail(x, n=1, ...)}.
+  }
 \usage{
-first(x)
-last(x)
-\method{first}{default}(x)
-\method{last}{default}(x)
-\method{first}{list}(x)
-\method{last}{list}(x)
+first(x, n=1, ...)
+last(x, n=1, ...)
 }
-%- maybe also 'usage' for other objects documented here.
 \arguments{
-  \item{x}{vector or list}
+  \item{x}{data object}
+  \item{n}{a single integer. If positive, size for the resulting object:
+          number of elements for a vector (including lists), rows for a
+          matrix or data frame or lines for a function. If negative,
+          all but the ‘n’ last/first number of elements of ‘x’.}
+   \item{...}{arguments to be passed to or from other methods.}
 }
 \value{
-  The first or last element of \code{x}.
+  An object (usually) like ‘x’ but generally smaller.
 }
 \author{
   Gregory R. Warnes \email{gr...@wa...}
@@ -43,5 +40,16 @@
 l <- list(a=1, b=2, c=3)
 first(l)
 last(l)
+
+## and data.frames
+df <- data.frame(a=1:2, b=3:4, c=5:6)
+first(df)
+last(df)
+
+## and matrixes
+m <- as.matrix(df)
+first(m)
+last(m)
+
 }
 \keyword{ manip }

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