转换R中的数字

Question

我特别需要在R中"转换"一个数字.例如,

"floor"操作表现为:

138  -> 100
1233 -> 1000

"天花板"操作表现为:

138  -> 200
1233 -> 2000

在R中有一种简单的方法可以实现这一点吗？谢谢

Answer 1

你可以分别提取指数:

floorEx <- function(x) {
  ex <- 10^trunc(log10(x))
  return(trunc(x/ex)*ex)
}

ceilingEx <- function(x) {
  ex <- 10^trunc(log10(x))
  return(ceiling(x/ex)*ex)
}

例子:

floorEx(123)
# [1] 100

ceilingEx(123)
# [1] 200

ceilingEx(c(123, 1234, 12345))
# [1]   200  2000 20000

编辑:

• 使用trunc代替floor和集成旧的ex函数(ex <- function(x)floor(log10(x)))来加速计算一点点
• 添加基准来与@ eddi进行比较 floorR

风向标:

## provided by @eddi
floorR <- function(x) {r <- signif(x, 1); r - (r > x) * 10^trunc(log10(x))}

library("microbenchmark")

x <- 123; microbenchmark(floorEx(x), floorR(x), signif(x), times=1e4)
# Unit: nanoseconds
#        expr  min   lq median     uq    max neval
#  floorEx(x) 2182 2414   2521 2683.0 704190 10000
#   floorR(x) 2894 3150   3278 3505.5  22260 10000
#   signif(x)  372  472    507  556.0  10963 10000

x <- 1:1000; microbenchmark(floorEx(x), floorR(x), signif(x), times=1e2)
# Unit: microseconds
#        expr     min       lq   median       uq      max neval
#  floorEx(x) 100.560 101.2460 101.6945 115.6385  818.895   100
#   floorR(x) 354.848 355.4705 356.0420 375.9210 1074.582   100
#   signif(x) 114.608 115.2120 115.4695 119.1805  186.738   100

Answer 2

它没有直接回答你的问题,但你也可以看看signif:

R> x <- 138
R> signif(x,1)
[1] 100
R> x <- 1712
R> signif(x,1)
[1] 2000

Answer 3

另外一个选项:

floor2 <- function(x) {
    mag <- 10^(nchar(round(x))-1)
    (x %/% mag) * mag
}

ceil2 <- function(x) {
    mag <- 10^(nchar(round(x))-1)
    ((x + mag) %/% mag) * mag
}