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, ...)

     ## Default S3 method:
     merge(x, y, ...)

     ## S3 method for class 'data.frame':
     merge(x, y, by = intersect(names(x), names(y)),
           by.x = by, by.y = by, all = FALSE, all.x = all, all.y = all,
           sort = TRUE, suffixes = c(".x",".y"), incomparables = NULL, ...)

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.

incomparables: values which cannot be matched.  See 'match'.

     ...: arguments to be passed to or from methods.

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.  For the precise meaning of
     'match', see 'match'.

     If 'by' or both 'by.x' and 'by.y' are of length 0 (a length zero
     vector or 'NULL'), the result, 'r', is the _Cartesian product_ of
     'x' and 'y', i.e., 'dim(r) = c(nrow(x)*nrow(y), 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.

     The complexity of the algorithm used is proportional to the length
     of the answer.

     In SQL database terminology, the default value of 'all = FALSE'
     gives a _natural join_, a special case of an _inner join_.
     Specifying 'all.x = TRUE' gives a _left (outer) join_, 'all.y =
     TRUE' a _right (outer) join_, and both ('all=TRUE' a _(full) outer
     join_.  DBMSes do not match 'NULL' records, equivalent to
     'incomparables = NA' in R.

Value:

     A data frame.  The rows are by default lexicographically sorted on
     the common columns, but for 'sort = FALSE' are in an unspecified
     order. 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 character column called 'Row.names'
     is added at the left, and in all cases the result has 'automatic'
     row names.

See Also:

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

Examples:

     ## use character columns of names to get sensible sort order
     authors <- data.frame(
         surname = I(c("Tukey", "Venables", "Tierney", "Ripley", "McNeil")),
         nationality = c("US", "Australia", "US", "UK", "Australia"),
         deceased = c("yes", rep("no", 4)))
     books <- data.frame(
         name = I(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)

     ## example of using 'incomparables'
     x <- data.frame(k1=c(NA,NA,3,4,5), k2=c(1,NA,NA,4,5), data=1:5)
     y <- data.frame(k1=c(NA,2,NA,4,5), k2=c(NA,NA,3,4,5), data=1:5)
     merge(x, y, by=c("k1","k2")) # NA's match
     merge(x, y, by=c("k1","k2"), incomparables=NA)
     merge(x, y, by="k1") # NA's match, so 6 rows
     merge(x, y, by="k2", incomparables=NA) # 2 rows

