Comparison.Rd 5.1 KB
 Radford Neal committed May 18, 2013 1 2 % File src/library/base/man/Comparison.Rd % Part of the R package, http://www.R-project.org  Radford Neal committed Aug 26, 2016 3 % Copyright 1995-2009 R Core Team  Radford Neal committed May 18, 2013 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 % Distributed under GPL 2 or later \name{Comparison} \alias{<} \alias{<=} \alias{==} \alias{!=} \alias{>=} \alias{>} \alias{Comparison} \alias{collation} \title{Relational Operators} \description{ Binary operators which allow the comparison of values in atomic vectors. } \usage{ x < y x > y x <= y x >= y x == y x != y } \arguments{ \item{x, y}{atomic vectors, symbols, calls, or other objects for which methods have been written.} } \details{ The binary comparison operators are generic functions: methods can be written for them individually or via the \code{\link[=S3groupGeneric]{Ops}}) group generic function. (See \code{\link[=S3groupGeneric]{Ops}} for how dispatch is computed.) Comparison of strings in character vectors is lexicographic within the strings using the collating sequence of the locale in use: see \code{\link{locales}}. The collating sequence of locales such as \samp{en_US} is normally different from \samp{C} (which should use ASCII) and can be surprising. Beware of making \emph{any} assumptions about the collation order: e.g. in Estonian \code{Z} comes between \code{S} and \code{T}, and collation is not necessarily character-by-character -- in Danish \code{aa} sorts as a single letter, after \code{z}. In Welsh \code{ng} may or may not be a single sorting unit: if it is it follows \code{g}. Some platforms may not respect the locale and always sort in numerical order of the bytes in an 8-bit locale, or in Unicode point order for a UTF-8 locale (and may not sort in the same order for the same language in different character sets). Collation of non-letters (spaces, punctuation signs, hyphens, fractions and so on) is even more problematic. Character strings can be compared with different marked encodings (see \code{\link{Encoding}}): they are translated to UTF-8 before comparison. At least one of \code{x} and \code{y} must be an atomic vector, but if the other is a list \R attempts to coerce it to the type of the atomic vector: this will succeed if the list is made up of elements of length one that can be coerced to the correct type. If the two arguments are atomic vectors of different types, one is coerced to the type of the other, the (decreasing) order of precedence being character, complex, numeric, integer, logical and raw. Missing values (\code{\link{NA}}) and \code{\link{NaN}} values are regarded as non-comparable even to themselves, so comparisons involving them will always result in \code{NA}. Missing values can also result when character strings are compared and one is not valid in the current collation locale. Language objects such as symbols and calls are deparsed to character strings before comparison. } \value{ A logical vector indicating the result of the element by element comparison. The elements of shorter vectors are recycled as necessary. Objects such as arrays or time-series can be compared this way provided they are conformable. } \note{ Do not use \code{==} and \code{!=} for tests, such as in \code{if} expressions, where you must get a single \code{TRUE} or \code{FALSE}. Unless you are absolutely sure that nothing unusual can happen, you should use the \code{\link{identical}} function instead. For numerical and complex values, remember \code{==} and \code{!=} do not allow for the finite representation of fractions, nor for rounding error. Using \code{\link{all.equal}} with \code{identical} is almost always preferable. See the examples. } \section{S4 methods}{ These operators are members of the S4 \code{\link{Compare}} group generic, and so methods can be written for them individually as well as for the group generic (or the \code{Ops} group generic), with arguments \code{c(e1, e2)}. } \references{ Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) \emph{The New S Language}. Wadsworth & Brooks/Cole. Collation of character strings is a complex topic. For an introduction see \url{http://en.wikipedia.org/wiki/Collating_sequence}. The \emph{Unicode Collation Algorithm} (\url{http://unicode.org/reports/tr10/}) is likely to be increasingly influential. Where available \R makes use of ICU (\url{http://site.icu-project.org/} for collation. } \seealso{ \code{\link{factor}} for the behaviour with factor arguments. \code{\link{Syntax}} for operator precedence. \code{\link{icuSetCollate}} to tune the string collation algorithm when ICU is in use. } \examples{ x <- stats::rnorm(20) x < 1 x[x > 0] x1 <- 0.5 - 0.3 x2 <- 0.3 - 0.1 x1 == x2 # FALSE on most machines identical(all.equal(x1, x2), TRUE) # TRUE everywhere \donttest{  Radford Neal committed May 18, 2013 133 134 # range of most 8-bit charsets, as well as of Latin-1 in Unicode z <- c(32:126, 160:255)  Radford Neal committed May 18, 2013 135 136 137 138 139 140 141 142 143 x <- if(l10n_info()\$MBCS) { intToUtf8(z, multiple = TRUE) } else rawToChar(as.raw(z), multiple= TRUE) ## by number writeLines(strwrap(paste(x, collapse=" "), width = 60)) ## by locale collation writeLines(strwrap(paste(sort(x), collapse=" "), width = 60)) }} \keyword{logic}