approxfun values

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
", header = TRUE)

f <- approxfun(dat)
x <- dat$V1[is.na(dat$V2)]
y <- f(x)
y


Hope this helps,

Rui Barradas

Em 14-02-2013 08:43, e-letter escreveu:

Readers,

According to the help '?approxfun', the function can be used to obtain
the interpolated values. The following test was tried:

testinterpolation<-read.csv('test.csv',header=FALSE)
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