# [R] approxfun values

Keith Jewell k.jewell at campden.co.uk
Thu Feb 14 13:10:10 CET 2013

```Alternatively, with approx() use xout to specify which interpolated
values you want returned:

approx(dat, xout=dat\$V1[is.na(dat\$V2)])

KJ

On 14/02/2013 11:43, Rui Barradas wrote:
> Hello,
>
> In what follows I've changed your df name to 'dat', to save some
> keystrokes.
> approxfun returns a function, so if you want just the interpolated
> values, apply that function to the x values where y is NA.
>
>
>
> dat <- read.table(text = "
> V1 V2
> 1 10 2
> 2 20 NA
> 3 30 5
> 4 40 7
> 5 50 NA
> 6 60 NA
> 7 70 2
> 8 80 6
> 9 90 9
> 10 100 NA
>
> f <- approxfun(dat)
> x <- dat\$V1[is.na(dat\$V2)]
> y <- f(x)
> y
>
>
> Hope this helps,
>
>
> Em 14-02-2013 08:43, e-letter escreveu:
>>
>> According to the help '?approxfun', the function can be used to obtain
>> the interpolated values. The following test was tried:
>>
>>> testinterpolation
>> V1 V2
>> 1 10 2
>> 2 20 NA
>> 3 30 5
>> 4 40 7
>> 5 50 NA
>> 6 60 NA
>> 7 70 2
>> 8 80 6
>> 9 90 9
>> 10 100 NA
>>> testinterpolationvalues<-approxfun(testinterpolation,y=NULL)
>>> testinterpolationvalues
>> function (v)
>> .C(C_R_approxfun, as.double(x), as.double(y), as.integer(n),
>> xout = as.double(v), as.integer(length(v)), as.integer(method),
>> as.double(yleft), as.double(yright), as.double(f), NAOK = TRUE,
>> PACKAGE = "stats")\$xout
>> <bytecode: 0x33ffab84>
>> <environment: 0x34072eac>
>>> testinterpolationvalues<-approx(testinterpolation,y=NULL)
>>> testinterpolationvalues
>> \$x
>> [1] 10.00000 11.63265 13.26531 14.89796 16.53061 18.16327 19.79592
>> 21.42857
>> [9] 23.06122 24.69388 26.32653 27.95918 29.59184 31.22449 32.85714
>> 34.48980
>> [17] 36.12245 37.75510 39.38776 41.02041 42.65306 44.28571 45.91837
>> 47.55102
>> [25] 49.18367 50.81633 52.44898 54.08163 55.71429 57.34694 58.97959
>> 60.61224
>> [33] 62.24490 63.87755 65.51020 67.14286 68.77551 70.40816 72.04082
>> 73.67347
>> [41] 75.30612 76.93878 78.57143 80.20408 81.83673 83.46939 85.10204
>> 86.73469
>> [49] 88.36735 90.00000
>>
>> \$y
>> [1] 2.000000 2.244898 2.489796 2.734694 2.979592 3.224490 3.469388
>> 3.714286
>> [9] 3.959184 4.204082 4.448980 4.693878 4.938776 5.244898 5.571429
>> 5.897959
>> [17] 6.224490 6.551020 6.877551 6.829932 6.557823 6.285714 6.013605
>> 5.741497
>> [25] 5.469388 5.197279 4.925170 4.653061 4.380952 4.108844 3.836735
>> 3.564626
>> [33] 3.292517 3.020408 2.748299 2.476190 2.204082 2.163265 2.816327
>> 3.469388
>> [41] 4.122449 4.775510 5.428571 6.061224 6.551020 7.040816 7.530612
>> 8.020408
>> [49] 8.510204 9.000000
>>
>> How to obtain a vector consisting _only_ of the interpolated values?
>>
>> It was expected that 'approx' would return both original and
>> interpolated values (which the above shows) and that 'approxfun' would
>> not show the original values.
>>
>> --
>> r2151
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help