Smisc (version 0.3.9.1)

select: Select rows or columns from data frames or matrices while always returning a data frame or a matrix

Description

The primary contribution of this function is that if a single row or column is selected, the object that is returned will be a matrix or a dataframe---and it will not be collapsed into a single vector, as is the usual behavior in R.

Usage

select(data, selection, cols = TRUE)

Arguments

data

A matrix or dataframe from whence data will be selected

selection

A character vector with column (or row) names, or, a numeric vector with column (or row) indexes.

cols

A logical, that when TRUE, indicates that columns will be selected. If FALSE, rows will be selected.

Value

The matrix or data frame is returned with the selected columns or rows.

Details

Selecting no rows or no columns is possible if selection = 0 or if length(selection) == 0. In this case, a data frame or matrix with either 0 columns or 0 rows is returned.

Examples

# NOT RUN {
# Consider this data frame
d <- data.frame(a = 1:5, b = rnorm(5), c = letters[1:5], d = factor(6:10),
                row.names = LETTERS[1:5], stringsAsFactors = FALSE)

# We get identical behavior when selecting more than one column
d1 <- d[, c("d", "c")]
d1c <- select(d, c("d", "c"))
d1
d1c
identical(d1, d1c)

# Different behavior when selecting a single column
d[,"a"]
select(d, "a")

# We can also select using numeric indexes
select(d, 1)

# Selecting a single row from a data frame produces results identical to default R behavior
d2 <- d[2,]
d2c <- select(d, "B", cols = FALSE)
identical(d2, d2c)

# Now consider a matrix
m <- matrix(rnorm(20), nrow = 4, dimnames = list(LETTERS[1:4], letters[1:5]))

# Column selection with two or more or more columns is equivalent to default R behavior
m1 <- m[,c(4, 3)]
m1c <- select(m, c("d", "c"))
m1
m1c
identical(m1, m1c)

# Selecting a single column returns a matrix of 1 column instead of a vector
m[,2]
select(m, 2)

# Selecting a single row returns a matrix of 1 row instead of a vector
m2 <- m["C",]
m2c <- select(m, "C", cols = FALSE)
m2
m2c
is.matrix(m2)
is.matrix(m2c)

# Selecting no rows or no columns occurs if 0 or an object of length 0
# is passed to 'selection'
select(d, 0)
select(d, which("bizarre" %in% colnames(d)))
select(d, 0, cols = FALSE)
# }