Tom Wenseleers - 2 years ago 75

R Question

In Mathematica there is the command

`Clip[x, {min, max}]`

which gives

`x`

`min<=x<=max`

`min`

`x<min`

`max`

`x>max`

http://reference.wolfram.com/mathematica/ref/Clip.html (mirror)

What would be the equivalent command for this in R? Ideally it should be a function that is listable, and that would either take a single value, or vector or a matrix as an argument?

I'm sure it must be easy, but I just couldn't find it anywhere... (and my own function I wrote to do this is a bit slow)

cheers,

Tom

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Answer Source

`Rcpp`

has `clamp`

for this:

```
cppFunction('NumericVector rcpp_clip( NumericVector x, double a, double b){
return clamp( a, x, b ) ;
}')
```

Here is a quick benchmark showing how it performs against other methods discussed :

```
pmin_pmax_clip <- function(x, a, b) pmax(a, pmin(x, b) )
ifelse_clip <- function(x, a, b) {
ifelse(x <= a, a, ifelse(x >= b, b, x))
}
operations_clip <- function(x, a, b) {
a + (x-a > 0)*(x-a) - (x-b > 0)*(x-b)
}
x <- rnorm( 10000 )
require(microbenchmark)
microbenchmark(
pmin_pmax_clip( x, -2, 2 ),
rcpp_clip( x, -2, 2 ),
ifelse_clip( x, -2, 2 ),
operations_clip( x, -2, 2 )
)
# Unit: microseconds
# expr min lq median uq max
# 1 ifelse_clip(x, -2, 2) 2809.211 3812.7350 3911.461 4481.0790 43244.543
# 2 operations_clip(x, -2, 2) 228.282 248.2500 266.605 1120.8855 40703.937
# 3 pmin_pmax_clip(x, -2, 2) 260.630 284.0985 308.426 336.9280 1353.721
# 4 rcpp_clip(x, -2, 2) 65.413 70.7120 84.568 92.2875 1097.039
```

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