R- Understading NA values in the result of akima::interp

问题

I have the following data frame

 ref_dat
             k Intensity Slope
1  0.021467214        33    16
2  0.012444759        33     8
3  0.006079156        33     4
4  0.003792025        33     2
5  0.022765086        47    16
6  0.017335375        47     8
7  0.007279113        47     4
8  0.003396341        47     2
9  0.034101951        75    16
10 0.023045525        75     8
11 0.009163758        75     4
12 0.003253822        75     2
13 0.039832629       110    16
14 0.029826826       110     8
15 0.010529787       110     4
16 0.002945170       110     2
17 0.042140630       155    16
18 0.032338534       155     8
19 0.013758171       155     4
20 0.002605399       155     2

I am trying to get the interpolated (and extrapolated) values of k for a given set of slope and intensity using interp function in akima, so I am doing the following.

my new slope

s=10

my new intensities

i=c(seq(0,50,5),rev(seq(0,50,5)))

and calculating new k values

k_new=interp(x=ref_dat$Intensity,y=ref_dat$Slope,z=ref_dat$k,xo=i,yo=s,extrap = FALSE)$z

and the result is

k_new
            [,1]
 [1,]         NA
 [2,]         NA
 [3,]         NA
 [4,]         NA
 [5,]         NA
 [6,]         NA
 [7,]         NA
 [8,] 0.01539903
 [9,] 0.01714568
[10,] 0.01850739
[11,] 0.01930460
[12,] 0.01930460
[13,]         NA
[14,]         NA
[15,]         NA
[16,]         NA
[17,]         NA
[18,]         NA
[19,]         NA
[20,]         NA
[21,]         NA
[22,]         NA

turning extrapolation on

k_new_ext=interp(x=ref_dat$Intensity,y=ref_dat$Slope,z=ref_dat$k,xo=i,yo=s,extrap = TRUE)$z

and the reult

k_new_ext
            [,1]
 [1,]         NA
 [2,]         NA
 [3,]         NA
 [4,]         NA
 [5,]         NA
 [6,]         NA
 [7,]         NA
 [8,] 0.01539903
 [9,] 0.01714568
[10,] 0.01850739
[11,] 0.01930460
[12,] 0.01930460
[13,]         NA
[14,]         NA
[15,]         NA
[16,]         NA
[17,]         NA
[18,]         NA
[19,]         NA
[20,]         NA
[21,]         NA
[22,]         NA

exploring the result a bit

cbind(i,k_new,k_new_ext)
       i                      
 [1,]  0         NA         NA
 [2,]  5         NA         NA
 [3,] 10         NA         NA
 [4,] 15         NA         NA
 [5,] 20         NA         NA
 [6,] 25         NA         NA
 [7,] 30         NA         NA
 [8,] 35 0.01539903 0.01539903
 [9,] 40 0.01714568 0.01714568
[10,] 45 0.01850739 0.01850739
[11,] 50 0.01930460 0.01930460
[12,] 50 0.01930460 0.01930460
[13,] 45         NA         NA
[14,] 40         NA         NA
[15,] 35         NA         NA
[16,] 30         NA         NA
[17,] 25         NA         NA
[18,] 20         NA         NA
[19,] 15         NA         NA
[20,] 10         NA         NA
[21,]  5         NA         NA
[22,]  0         NA         NA

Why I am getting NA values, even when the new intensity values are with in the range of values in ref_dat? Making extrap=TRUE doesn't solve my problem either.

来源：https://stackoverflow.com/questions/43003065/r-understading-na-values-in-the-result-of-akimainterp

标签

interpolation