From interp() Result, Produce 3-column Matrix

From an interp() result, produce a 3-column matrix or data.frame cbind(x, y, z).

interp2xyz(al, data.frame = FALSE)

Arguments

al

a list as produced from interp().

data.frame

logical indicating if result should be data.frame or matrix (default).

Value

a matrix (or data.frame) with three columns, called "x", "y", "z".

Author

Martin Maechler, Jan.18, 2013

See also

expand.grid() is the “essential ingredient” of interp2xyz().

interp.

Examples

data(akima)
ak.spl <- with(akima, interp(x, y, z, method = "akima"))
str(ak.spl)# list (x[i], y[j], z = <matrix>[i,j])
#> List of 3
#>  $ x: num [1:40] 0 0.641 1.282 1.923 2.564 ...
#>  $ y: num [1:40] 0 0.513 1.026 1.538 2.051 ...
#>  $ z: num [1:40, 1:40] 58.2 55.3 52.4 49.5 46.7 ...

## Now transform to simple  (x,y,z)  matrix / data.frame :
str(am <- interp2xyz(ak.spl))
#>  num [1:1600, 1:3] 0 0.641 1.282 1.923 2.564 ...
#>  - attr(*, "dimnames")=List of 2
#>   ..$ : NULL
#>   ..$ : chr [1:3] "x" "y" "z"
str(ad <- interp2xyz(ak.spl, data.frame=TRUE))
#> 'data.frame':	1600 obs. of  3 variables:
#>  $ x: num  0 0.641 1.282 1.923 2.564 ...
#>  $ y: num  0 0 0 0 0 0 0 0 0 0 ...
#>  $ z: num  58.2 55.3 52.4 49.5 46.7 ...
## and they are the same:
stopifnot( am == ad | (is.na(am) & is.na(ad)) )