参见R的帮助文件：help(ceiling) or help(floor)。搜索结果如下：
Rounding of Numbers
Description
ceiling takes a single numeric argument x and returns a numeric vector containing the smallest integers not less than the corresponding elements of x.
floor takes a single numeric argument x and returns a numeric vector containing the largest integers not greater than the corresponding elements of x.
trunc takes a single numeric argument x and returns a numeric vector containing the integers formed by truncating the values in x toward 0.
round rounds the values in its first argument to the specified number of decimal places (default 0).
signif rounds the values in its first argument to the specified number of significant digits.
zapsmall determines a digits argument dr for calling round(x, digits = dr) such that values close to zero (compared with the maximal absolute value) are ‘zapped’, i.e., treated as 0.
Usage
ceiling(x) floor(x) trunc(x, ...) round(x, digits = 0) signif(x, digits = 6) zapsmall(x, digits = getOption("digits")) Arguments
x | a numeric vector. A complex vector is allowed for round, signif and zapsmall. |
digits | integer indicating the precision to be used. |
... | arguments to be passed to methods. |
Details
All but zapsmall are generic functions: methods can be defined for them individually or via the Math group generic.
Note that for rounding off a 5, the IEC 60559 standard is expected to be used, ‘go to the even digit’. Therefore round(0.5) is 0 and round(-1.5) is -2. However, this is dependent on OS services and on representation error (since e.g. 0.15 is not represented exactly, the rounding rule applies to the represented number and not to the printed number, and so round(0.15, 1) could be either 0.1 or 0.2).
For signif the recognized values of digits are 1...22. Complex numbers are rounded to retain the specified number of digits in the larger of the components. Each element of the vector is rounded individually, unlike printing.
All except zapsmall are primitive, but as from R 2.7.0 arguments are matched by name in round and signif (whereas the default method for ceiling, floor and trunc ignore argument names).
S4 methods
ceiling, floor and trunc are S4 generic and members of the Math group generic. As an S4 generic, trunc has only one argument.
round and signif are S4 generic and members of the Math2 group generic.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole. (Except zapsmall.)
Chambers, J. M. (1998) Programming with Data. A Guide to the S Language. Springer. (zapsmall.)
See Also
as.integer.
Examples
round(.5 + -2:4) # IEEE rounding: -2 0 0 2 2 4 4 ( x1 <- seq(-2, 4, by = .5) ) round(x1)#-- IEEE rounding ! x1[trunc(x1) != floor(x1)] x1[round(x1) != floor(x1 + .5)] (non.int <- ceiling(x1) != floor(x1)) x2 <- pi * 100^(-1:3) round(x2, 3) signif(x2, 3) print (x2 / 1000, digits=4) zapsmall(x2 / 1000, digits=4) zapsmall(exp(1i*0:4*pi/2))
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