XStringViews-class {Biostrings} | R Documentation

## The XStringViews class

### Description

The XStringViews class is the basic container for storing a set of views (start/end locations) on the same sequence (an XString object).

### Details

An XStringViews object contains a set of views (start/end locations) on the same XString object called "the subject string" or "the subject sequence" or simply "the subject". Each view is defined by its start and end locations: both are integers such that start <= end. An XStringViews object is in fact a particular case of an IRanges object (the XStringViews class contains the IRanges class) so it can be manipulated in the same way: see IRanges for more information. Note that two views can overlap and that a view can be "out of limits" i.e. it can start before the first letter of the subject or/and end after its last letter.

### Accesor methods

In the code snippets below, `x` is an XStringViews object.

  `subject(x)`: The subject of `x`. This is always an XString object.
  `nchar(x)`: A vector of non-negative integers containing the number of letters in each view. Values in `nchar(x)` coincide with values in `width(x)` except for "out of limits" views where they are lower.

### Other methods

In the code snippets below, `x`, `object`, `e1` and `e2` are XStringViews objects, and `i` can be a numeric or logical vector.

  `x[[i]]`: Extract a view as an XString object. `i` must be a single numeric value (a numeric vector of length 1). Can't be used for extracting a view that is "out of limits" (raise an error). The returned object has the same XString subtype as `subject(x)`.
  `e1 == e2`: A vector of logicals indicating the result of the view by view comparison. The views in the shorter of the two XStringViews object being compared are recycled as necessary.

  Like for comparison between XString objects, comparison between two XStringViews objects with subjects of different classes is not supported with one exception: when the subjects are DNAString and RNAString instances.

  Also, like with XString objects, comparison between an XStringViews object with a BString subject and a character vector is supported (see examples below).

  `e1 != e2`: Equivalent to `!(e1 == e2)`.
  `as.character(x, use.names, check.limits)`: Convert `x` to a character vector of the same length as `x`. `use.names` controls whether or not `desc(x)` should be used to set the names of the returned vector (default is `TRUE`). `check.limits` controls whether or not an error should be raised if `x` contains "out of limit" views (default is `TRUE`). With `check.limits=FALSE` then "out of limit" views are padded with spaces.
  `as.matrix(x, mode, use.names, check.limits)`: Depending on what `mode` is choosen (`"integer"` or `"character"`), return either a 2-column integer matrix containing `start(x)` and `end(x)` or a character matrix containing the "exploded" representation of the views. `mode="character"` can only be used on an XStringViews object with equal-width views. Arguments `use.names` and `check.limits` are ignored with `mode="integer"`. With `mode="character"`, `use.names` controls whether or not `desc(x)` should be used to set the row names of the returned matrix (default is `TRUE`), and `check.limits` controls whether or not an error should be raised if `x` contains "out of limit" views (default is `TRUE`). With `check.limits=FALSE` then "out of limit" views are padded with spaces.
  `as.list(x)`: Convert `x` to a list of XString objects. Can't be used if `x` has "out of limits" views (raise an error).
  `toString(x)`: Equivalent to `toString(as.character(x))`.

### Author(s)

H. Pages

### See Also

IRanges-class, XStringViews-constructors, XString-class, XStringSet-class, `letter`

### Examples

      ## One standard way to create an XStringViews object is to use
      ## the "views" constructor:
      s <- DNAString("-CTC-N")
      v4 <- views(s, 3:0, 5:8)
      v4
      subject(v4)
      length(v4)
      start(v4)
      end(v4)
      width(v4)

      ## Attach a comment to views #3 and #4:
      desc(v4)[3:4] <- "out of limits"
      desc(v4)

      ## A more programatical way to "tag" the "out of limits" views:
      desc(v4)[start(v4) < 1 | nchar(subject(v4)) < end(v4)] <- "out of limits"
      ## or just:
      desc(v4)[nchar(v4) < width(v4)] <- "out of limits"

      ## Two equivalent ways to extract a view as an XString object:
      s2a <- v4[[2]]
      s2b <- subXString(subject(v4), start(v4)[2], end(v4)[2])
      identical(s2a, s2b) # TRUE

      ## It is an error to try to extract an "out of limits" view:
      #v4[[3]] # Error!

      v12 <- views(DNAString("TAATAATG"), -2:9, 0:11)
      v12 == DNAString("TAA")
      v12[v12 == v12[4]]
      v12[v12 == v12[1]]
      v12[3] == views(RNAString("AU"), 0, 2)

      ## Here the first view doesn't even overlap with the subject:
      views(BString("aaa--b"), -3:4, -3:4 + c(3:6, 6:3))

[Package Biostrings version 2.8.18 Index]