Vector-comparison {S4Vectors} | R Documentation

## Compare, order, tabulate vector-like objects

### Description

Generic functions and methods for comparing, ordering, and tabulating vector-like objects.

### Usage

    ## Element-wise (aka "parallel") comparison of 2 Vector objects
    ## ------------------------------------------------------------

    pcompare(x, y)

    ## S4 method for signature 'Vector,Vector'
    e1 == e2
    ## S4 method for signature 'Vector,ANY'
    e1 == e2
    ## S4 method for signature 'ANY,Vector'
    e1 == e2

    ## S4 method for signature 'Vector,Vector'
    e1 <= e2
    ## S4 method for signature 'Vector,ANY'
    e1 <= e2
    ## S4 method for signature 'ANY,Vector'
    e1 <= e2

    ## S4 method for signature 'Vector,Vector'
    e1 != e2
    ## S4 method for signature 'Vector,ANY'
    e1 != e2
    ## S4 method for signature 'ANY,Vector'
    e1 != e2

    ## S4 method for signature 'Vector,Vector'
    e1 >= e2
    ## S4 method for signature 'Vector,ANY'
    e1 >= e2
    ## S4 method for signature 'ANY,Vector'
    e1 >= e2

    ## S4 method for signature 'Vector,Vector'
    e1 < e2
    ## S4 method for signature 'Vector,ANY'
    e1 < e2
    ## S4 method for signature 'ANY,Vector'
    e1 < e2

    ## S4 method for signature 'Vector,Vector'
    e1 > e2
    ## S4 method for signature 'Vector,ANY'
    e1 > e2
    ## S4 method for signature 'ANY,Vector'
    e1 > e2

    ## selfmatch()
    ## -----------

    selfmatch(x, ...)

    ## duplicated() & unique()
    ## -----------------------

    ## S4 method for signature 'Vector'
    duplicated(x, incomparables=FALSE, ...)

    ## S4 method for signature 'Vector'
    unique(x, incomparables=FALSE, ...)

    ## %in%
    ## ----

    ## S4 method for signature 'Vector,Vector'
    x %in% table
    ## S4 method for signature 'Vector,ANY'
    x %in% table
    ## S4 method for signature 'ANY,Vector'
    x %in% table

    ## findMatches() & countMatches()
    ## ------------------------------

    findMatches(x, table, select=c("all", "first", "last"), ...)
    countMatches(x, table, ...)

    ## rank()
    ## ------

    ## S4 method for signature 'Vector'
    rank(x, na.last = TRUE, ties.method = c("average",
            "first", "last", "random", "max", "min"), by)

    ## sort()
    ## ------

    ## S4 method for signature 'Vector'
    sort(x, decreasing=FALSE, na.last=NA, by)

    ## table()
    ## -------

    ## S4 method for signature 'Vector'
    table(...)

### Arguments

`x, y, e1, e2, table` | Vector-like objects.
`incomparables` | The `duplicated` method for Vector objects does NOT support this argument. The `unique` method for Vector objects, which is implemented on top of `duplicated`, propagates this argument to its call to `duplicated`. See `?base::duplicated` and `?base::unique` for more information about this argument.
`select` | Only `select="all"` is supported at the moment. Note that you can use `match` if you want to do `select="first"`. Otherwise you're welcome to request this on the Bioconductor mailing list.
`ties.method` | See `?base::rank`.
`decreasing, na.last` | See `?base::sort`.
`by` | A formula referencing the metadata columns by which to sort, e.g., `~ x + y` sorts by column “x”, breaking ties with column “y”.
`...` | A Vector object for `table` (the `table` method for Vector objects can only take one input object). Otherwise, extra arguments supported by specific methods. In particular: The default `selfmatch` method, which is implemented on top of `match`, propagates the extra arguments to its call to `match`. The `duplicated` method for Vector objects, which is implemented on top of `selfmatch`, accepts extra argument `fromLast` and propagates the other extra arguments to its call to `selfmatch`. See `?base::duplicated` for more information about this argument. The `unique` method for Vector objects, which is implemented on top of `duplicated`, propagates the extra arguments to its call to `duplicated`. The default `findMatches` and `countMatches` methods, which are implemented on top of `match` and `selfmatch`, propagate the extra arguments to their calls to `match` and `selfmatch`. The `sort` method for Vector objects, which is implemented on top of `order`, only accepts extra argument `na.last` and propagates it to its call to `order`.

### Details

Doing `pcompare(x, y)` on 2 vector-like objects `x` and `y` of length 1 must return an integer less than, equal to, or greater than zero if the single element in `x` is considered to be respectively less than, equal to, or greater than the single element in `y`. If `x` or `y` have a length != 1, then they are typically expected to have the same length so `pcompare(x, y)` can operate element-wise, that is, in that case it returns an integer vector of the same length as `x` and `y` where the i-th element is the result of compairing `x[i]` and `y[i]`. If `x` and `y` don't have the same length and are not zero-length vectors, then the shortest is first recycled to the length of the longest. If one of them is a zero-length vector then `pcompare(x, y)` returns a zero-length integer vector.

`selfmatch(x, ...)` is equivalent to `match(x, x, ...)`. This is actually how the default method is implemented. However note that `selfmatch(x, ...)` will typically be more efficient than `match(x, x, ...)` on vector-like objects for which a specific `selfmatch` method is implemented.

`findMatches` is an enhanced version of `match` which, by default (i.e. if `select="all"`), returns all the matches in a Hits object.

`countMatches` returns an integer vector of the length of `x` containing the number of matches in `table` for each element in `x`.

### Value

For `pcompare`: see Details section above.

For `selfmatch`: an integer vector of the same length as `x`.

For `duplicated`, `unique`, and `%in%`: see `?BiocGenerics::duplicated`, `?BiocGenerics::unique`, and `?`%in%``.

For `findMatches`: a Hits object by default (i.e. if `select="all"`).

For `countMatches`: an integer vector of the length of `x` containing the number of matches in `table` for each element in `x`.

For `sort`: see `?BiocGenerics::sort`.

For `table`: a 1D array of integer values promoted to the `"table"` class. See `?BiocGeneric::table` for more information.

### Note

The following notes are for developers who want to implement comparing, ordering, and tabulating methods for their own Vector subclass:

1. The 6 traditional binary comparison operators are: `==`, `!=`, `<=`, `>=`, `<`, and `>`. The S4Vectors package provides the following methods for these operators:

       setMethod("==", c("Vector", "Vector"),
           function(e1, e2) { pcompare(e1, e2) == 0L }
       )
       setMethod("<=", c("Vector", "Vector"),
           function(e1, e2) { pcompare(e1, e2) <= 0L }
       )
       setMethod("!=", c("Vector", "Vector"),
           function(e1, e2) { !(e1 == e2) }
       )
       setMethod(">=", c("Vector", "Vector"),
           function(e1, e2) { e2 <= e1 }
       )
       setMethod("<", c("Vector", "Vector"),
           function(e1, e2) { !(e2 <= e1) }
       )
       setMethod(">", c("Vector", "Vector"),
           function(e1, e2) { !(e1 <= e2) }
       )

   With these definitions, the 6 binary operators work out-of-the-box on Vector objects for which `pcompare` works the expected way. If `pcompare` is not implemented, then it's enough to implement `==` and `<=` methods to have the 4 remaining operators (`!=`, `>=`, `<`, and `>`) work out-of-the-box.

2. The S4Vectors package provides no `pcompare` method for Vector objects. Specific `pcompare` methods need to be implemented for specific Vector subclasses (e.g. for Hits and IntegerRanges objects). These specific methods must obey the rules described in the Details section above.

3. The `duplicated`, `unique`, and `%in%` methods for Vector objects are implemented on top of `selfmatch`, `duplicated`, and `match`, respectively, so they work out-of-the-box on Vector objects for which `selfmatch`, `duplicated`, and `match` work the expected way.

4. Also the default `findMatches` and `countMatches` methods are implemented on top of `match` and `selfmatch` so they work out-of-the-box on Vector objects for which those things work the expected way.

5. However, since `selfmatch` itself is also implemented on top of `match`, then having `match` work the expected way is actually enough to get `selfmatch`, `duplicated`, `unique`, `%in%`, `findMatches`, and `countMatches` work out-of-the-box on Vector objects.

6. The `sort` method for Vector objects is implemented on top of `order`, so it works out-of-the-box on Vector objects for which `order` works the expected way.

7. The `table` method for Vector objects is implemented on top of `selfmatch`, `order`, and `as.character`, so it works out-of-the-box on a Vector object for which those things work the expected way.

8. The S4Vectors package provides no `match` or `order` methods for Vector objects. Specific methods need to be implemented for specific Vector subclasses (e.g. for Hits and IntegerRanges objects).

### Author(s)

Hervé Pagès

### See Also

- The Vector class.

- Hits-comparison for comparing and ordering hits.

- Vector-setops for set operations on vector-like objects.

- Vector-merge for merging vector-like objects.

- IntegerRanges-comparison in the IRanges package for comparing and ordering ranges.

- `==` and `%in%` in the base package, and `BiocGenerics::match`, `BiocGenerics::duplicated`, `BiocGenerics::unique`, `BiocGenerics::order`, `BiocGenerics::sort`, `BiocGenerics::rank` in the BiocGenerics package for general information about the comparison/ordering operators and functions.

- The Hits class.

- `BiocGeneric::table` in the BiocGenerics package.

### Examples

    ## ---------------------------------------------------------------------
    ## A. SIMPLE EXAMPLES
    ## ---------------------------------------------------------------------

    y <- c(16L, -3L, -2L, 15L, 15L, 0L, 8L, 15L, -2L)
    selfmatch(y)

    x <- c(unique(y), 999L)
    findMatches(x, y)
    countMatches(x, y)

    ## See ?`IntegerRanges-comparison` for more examples (on IntegerRanges
    ## objects). You might need to load the IRanges package first.

    ## ---------------------------------------------------------------------
    ## B. FOR DEVELOPERS: HOW TO IMPLEMENT THE BINARY COMPARISON OPERATORS
    ##    FOR YOUR Vector SUBCLASS
    ## ---------------------------------------------------------------------

    ## The answer is: don't implement them. Just implement pcompare() and the
    ## binary comparison operators will work out-of-the-box. Here is an
    ## example:

    ## (1) Implement a simple Vector subclass.

    setClass("Raw", contains="Vector", representation(data="raw"))

    setMethod("length", "Raw", function(x) length(x@data))

    setMethod("[", "Raw",
        function(x, i, j, ..., drop) { x@data <- x@data[i]; x }
    )

    x <- new("Raw", data=charToRaw("AB.x0a-BAA+C"))
    stopifnot(identical(length(x), 12L))
    stopifnot(identical(x[7:3], new("Raw", data=charToRaw("-a0x."))))

    ## (2) Implement a "pcompare" method for Raw objects.

    setMethod("pcompare", c("Raw", "Raw"),
        function(x, y) {as.integer(x@data) - as.integer(y@data)}
    )

    stopifnot(identical(which(x == x[1]), c(1L, 9L, 10L)))
    stopifnot(identical(x[x < x[5]], new("Raw", data=charToRaw(".-+"))))

[Package S4Vectors version 0.18.3 Index]