| Comparison {base} | R Documentation |
Binary operators which allow the comparison of values in atomic vectors.
x < y x > y x <= y x >= y x == y x != y
x, y |
atomic vectors, symbols, calls, or other objects for which methods have been written. |
The binary comparison operators are generic functions: methods can be
written for them individually or via the
Ops) group generic function. (See
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
locales. The collating sequence of locales such as
en_US is normally different from C (which should use
ASCII) and can be surprising. Beware of making any assumptions
about the collation order: e.g. in Estonian Z comes between
S and T, and collation is not necessarily
character-by-character – in Danish aa sorts as a single
letter, after z. In Welsh ng may or may not be a single
sorting unit: if it is it follows 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.
At least one of x and 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 (NA) and NaN values are
regarded as non-comparable even to themselves, so comparisons
involving them will always result in 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.
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.
These operators are members of the S4 Compare group generic,
and so methods can be written for them individually as well as for the
group generic (or the Ops group generic), with arguments
c(e1, e2).
Do not use == and != for tests, such as in if
expressions, where you must get a single TRUE or
FALSE. Unless you are absolutely sure that nothing unusual
can happen, you should use the identical function
instead.
For numerical and complex values, remember == and != do
not allow for the finite representation of fractions, nor for rounding
error. Using all.equal with identical is almost
always preferable. See the examples.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Collation of character strings is a complex topic. For an introduction see http://en.wikipedia.org/wiki/Collating_sequence. The Unicode Collation Algorithm (http://unicode.org/reports/tr10/) is likely to be increasing influential.
factor for the behaviour with factor arguments.
Syntax for operator precedence.
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
z <- c(32:126, 160:255) # range of most 8-bit charsets, Latin-1 in Unicode
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))