dist {mva}

R Documentation

Distance Matrix Computation

Description

This function computes and returns the distance matrix computed by using the specified distance measure to compute the distances between the rows of a data matrix.

Usage

dist(x, method = "euclidean", diag = FALSE, upper = FALSE)

print.dist(x, diag = NULL, upper = NULL, ...)
as.matrix.dist(x)
as.dist(m, diag = FALSE, upper = FALSE)

Arguments

x	A matrix or (data frame). Distances between the rows of x will be computed.
method	The distance measure to be used. This must be one of "euclidean", "maximum", "manhattan", "canberra" or "binary". Any unambiguous substring can be given.
diag	A logical value indicating whether the diagonal of the distance matrix should be printed by print.dist.
upper	A logical value indicating whether the upper triangle of the distance matrix should be printed by print.dist.
m	A matrix of distances to be converted to a "dist" object (only the lower triangle is used, the rest is ignored).
...	further arguments, passed to the (next) print method.

Details

Available distance measures are (written for two vectors x and y):

euclidean:

Usual square distance between the two vectors (2 norm).

maximum:

Maximum distance between two components of x and y (supremum norm)

manhattan:

Absolute distance between the two vectors (1 norm).

canberra:

\sum_i |x_i - y_i| / |x_i + y_i|. Terms with zero numerator and denominator are omitted from the sum and treated as if the values were missing.

binary:

(aka asymmetric binary): The vectors are regarded as binary bits, so non-zero elements are ‘on’ and zero elements are ‘off’. The distance is the proportion of bits in which only one is on amongst those in which at least one is on.

Missing values are allowed, and are excluded from all computations involving the rows within which they occur. If some columns are excluded in calculating a Euclidean, Manhattan or Canberra distance, the sum is scaled up proportionally to the number of columns used. If all pairs are excluded when calculating a particular distance, the value is NA.

The functions as.matrix.dist() and as.dist() can be used for conversion between objects of class "dist" and conventional distance matrices and vice versa.

Value

An object of class "dist".

The lower triangle of the distance matrix stored by columns in a single vector. The vector has the attributes "Size", "Diag", "Upper", "Labels" and "class" equal to "dist".

References

Mardia, K. V., Kent, J. T. and Bibby, J. M. (1979) Multivariate Analysis. London: Academic Press.

See Also

hclust.

Examples

x <- matrix(rnorm(100), nrow=5)
dist(x)
dist(x, diag = TRUE)
dist(x, upper = TRUE)
m <- as.matrix(dist(x))
d <- as.dist(m)
stopifnot(d == dist(x))
names(d) <- LETTERS[1:5]
print(d, digits = 3)

## example of binary and canberra distances.
x <- c(0, 0, 1, 1, 1, 1)
y <- c(1, 0, 1, 1, 0, 1)
dist(rbind(x,y), method="binary")
## answer 0.4 = 2/5
dist(rbind(x,y), method="canberra")
## answer 2 * (6/5)