SSBtools (version 1.7.0)

Match: Matching rows in data frames

Description

The algorithm is based on converting variable combinations to whole numbers. The final matching is performed using match.

Usage

Match(x, y)

Value

An integer vector giving the position in y of the first match if there is a match, otherwise NA.

Arguments

x

data frame

y

data frame

Author

Øyvind Langsrud

Details

When the result of multiplying together the number of unique values in each column of x exceeds 9E15 (largest value stored exactly by the numeric data type), the algorithm is recursive.

Examples

a <- data.frame(x = c("a", "b", "c"), y = c("A", "B"), z = 1:6)
b <- data.frame(x = c("b", "c"), y = c("B", "K", "A", "B"), z = c(2, 3, 5, 6))

Match(a, b)
Match(b, a)

# Slower alternative
match(data.frame(t(a), stringsAsFactors = FALSE), data.frame(t(b), stringsAsFactors = FALSE))
match(data.frame(t(b), stringsAsFactors = FALSE), data.frame(t(a), stringsAsFactors = FALSE))

# More comprehensive example (n, m and k may be changed)
n <- 10^4
m <- 10^3
k <- 10^2
data(precip)
data(mtcars)
y <- data.frame(car = sample(rownames(mtcars), n, replace = TRUE), 
                city = sample(names(precip), n, replace = TRUE),
                n = rep_len(1:k, n), a = rep_len(c("A", "B", "C", "D"), n),
                b = rep_len(as.character(rnorm(1000)), n),
                d = sample.int(k + 10, n, replace = TRUE),
                e = paste(sample.int(k * 2, n, replace = TRUE), 
                          rep_len(c("Green", "Red", "Blue"), n), sep = "_"),
                r = rnorm(k)^99)
x <- y[sample.int(n, m), ]
row.names(x) <- NULL
ix <- Match(x, y)