sortFrame: Sort a data frame
In lsr: Companion to "Learning Statistics with R"

Description Usage Arguments Details Value See Also Examples

Sorts a data frame using one or more variables.

1	sortFrame(x, ..., alphabetical = TRUE)

`x`	Data frame to be sorted
`...`	A list of sort terms (see below)
`alphabetical`	Should character vectors be sorted alphabetically?

The simplest use of this function is to sort a data frame x in terms of one or more of the variables it contains. If for instance, the data frame x contains two variables a and b, then the command sortFrame(x,a,b) sorts by variable a, breaking ties using variable b. Numeric variables are sorted in ascending order: to sort in descending order of a and then ascending order of b, use the command sortFrame(x,-a,b). Factors are treated as numeric variables, and are sorted by the internal codes (i.e., the first factor level equals 1, the second factor levels equals 2 and so on). Character vectors are sorted in alphabetical order, which differs from the ordering used by the sort function; to use the default 'ascii' ordering, specify alphabetical=FALSE. Minus signs can be used in conjunction with character vectors in order to sort in reverse alphabetical order. If c represents a character variable, then sortFrame(x,c) sorts in alphabetical order, whereas sortFrame(x,-c) sorts in reverse alphabetical order.

It is also possible to specify more complicated sort terms by including expressions using multiple variables within a single term, but care is required. For instance, it is possible to sort the data frame by the sum of two variables, using the command sortFrame(x, a+b). For numeric variables expressions of this kind should work in the expected manner, but this is not always the case for non-numeric variables: sortFrame uses the xtfrm function to provide, for every variable referred to in the list of sort terms (...) a numeric vector that sorts in the same order as the original variable. This reliance is what makes reverse alphabetical order (e.g., sortFrame(x,-c)) work. However, it also means that it is possible to specify somewhat nonsensical sort terms for character vectors by abusing the numerical coding (e.g. sortFrame(x,(c-3)^2); see the examples section). It also means that sorting in terms of string operation functions (e.g., nchar) do not work as expected. See examples section. Future versions of sortFrame will (hopefully) address this, possibly by allowing the user to "switch off" the internal use of xtfrm, or else by allowing AsIs expressions to be used in sort terms.

The sorted data frame

sort, order, xtfrm

txt <- c("bob","Clare","clare","bob","eve","eve")
num1 <- c(3,1,2,0,0,2)
num2 <- c(1,1,3,0,3,2)
etc <- c("not","used","as","a","sort","term")
dataset <- data.frame( txt, num1, num2, etc, stringsAsFactors=FALSE )

sortFrame( dataset, num1 )
sortFrame( dataset, num1, num2 )
sortFrame( dataset, txt )