merge                  package:base                  R Documentation

Merge Two Data Frames

Description:

     Merge two data frames by common columns or row names, or do other
     versions of database ``join'' operations.

Usage:

     merge(x, y, by, by.x, by.y, all = FALSE, all.x = all, all.y = all,
           sort = TRUE, suffixes = c(".x",".y"))

Arguments:

    x, y: data frames, or objects to be coerced to one

by, by.x, by.y: specifications of the common columns. See Details.

     all: logical; `all=L' is shorthand for `all.x=L' and `all.y=L'.

   all.x: logical; if `TRUE', then extra rows will be added to the
          output, one for each row in `x' that has no matching row in
          `y'.  These rows will have `NA's in those columns that are
          usually filled with values from `y'.  The default is `FALSE',
          so that only rows with data from both `x' and `y' are
          included in the output.

   all.y: logical; analogous to `all.x' above.

    sort: logical.  Should the results be sorted on the `by' columns?

suffixes: character(2) specifying the suffixes to be used for making
          non-`by' `names()' unique.

Details:

     By default the data frames are merged on the columns with names
     they both have, but separate specifications of the columns can be
     given by `by.x' and `by.y'.  Columns can be specified by name,
     number or by a logical vector: the name `"row.names"' or the
     number `0' specifies the row names.  The rows in the two data
     frames that match on the specified columns are extracted, and
     joined together.  If there is more than one match, all possible
     matches contribute one row each.
     If the `by.*' vector are of length 0, the result, `r', is the
     ``Cartesian product'' of `x' and `y', i.e., `dim(r) =
     c(nrow(x)*nrow, ncol(x) + ncol(y))'.

     If `all.x' is true, all the non matching cases of `x' are appended
     to the result as well, with `NA' filled in the corresponding
     columns of `y';  analogously for `all.y'.

     If the remaining columns in the data frames have any common names,
     these have `suffixes' (`".x"' and `".y"' by default) appended to
     make the names of the result unique.

Value:

     A data frame.  The rows are by default lexicographically sorted on
     the common columns, but are otherwise in the order in which they
     occurred in `x'.  The columns are the common columns followed by
     the remaining columns in `x' and then those in `y'.  If the
     matching involved row names, an extra column `Row.names' is added
     at the left, and in all cases the result has no special row names.

See Also:

     `data.frame', `by', `cbind'

Examples:

     authors <- data.frame(
         surname = c("Tukey", "Venables", "Tierney", "Ripley", "McNeil"),
         nationality = c("US", "Australia", "US", "UK", "Australia"),
         deceased = c("yes", rep("no", 4)))
     books <- data.frame(
         name = c("Tukey", "Venables", "Tierney",
                  "Ripley", "Ripley", "McNeil", "R Core"),
         title = c("Exploratory Data Analysis",
                   "Modern Applied Statistics ...",
                   "LISP-STAT",
                   "Spatial Statistics", "Stochastic Simulation",
                   "Interactive Data Analysis",
                   "An Introduction to R"),
         other.author = c(NA, "Ripley", NA, NA, NA, NA,
                          "Venables & Smith"))

     (m1 <- merge(authors, books, by.x = "surname", by.y = "name"))
     (m2 <- merge(books, authors, by.x = "name", by.y = "surname"))
     stopifnot(as.character(m1[,1]) == as.character(m2[,1]),
               all.equal(m1[, -1], m2[, -1][ names(m1)[-1] ]),
               dim(merge(m1, m2, by = integer(0))) == c(36, 10))

     ## "R core" is missing from authors and appears only here :
     merge(authors, books, by.x = "surname", by.y = "name", all = TRUE)

