plyr (version 1.1)

join: Join two data frames together.

Description

Join two data frames together.

Usage

join(x, y, by=intersect(names(x), names(y)), type="left")

Arguments

x

data frame

y

data frame

by

character vector of variable names to join by

type

type of join: left (default), right, inner or full. See details for more information.

Details

Unlike merge, preserves the order of x no matter what join type is used. If needed, rows from y will be added to the bottom.

Join is about four times faster than merge, but it achieves this speed by being less flexible, and is designed for the types of problems where you would use a sql join.

The four join types return:

• inner: only rows with matching keys in both x and y
• left: all rows in x, adding matching columns from y
• right: all rows in y, adding matching columns from x
• full: all rows in x with matching columns in y, then the rows of y that don't match x.

Examples

first <- ddply(baseball, "id", summarise, first = min(year))
system.time(b2 <- merge(baseball, first, by = "id", all.x = TRUE))
system.time(b3 <- join(baseball, first, by = "id"))

b2 <- arrange(b2, id, year, stint)
b3 <- arrange(b3, id, year, stint)
stopifnot(all.equal(b2, b3))