[R] spline for implicit functions

[Casper Ti. Vector]

Hello list, is there any R function for generating spline for implicit
functions, for example a spline for an two-column data frame where for
one value for one variable there maybe several correspondent values for
another? Many thanks.

Currently I'm using this home-made one:
> spline2d <- function(df, ...)
> {
>     xname <- colnames(df)[1]
>     yname <- colnames(df)[2]
>
>     df <- data.frame(c(1 : nrow(df)), df[1], df[2])
>     colnames(df) <- c("index", xname, yname)
>
>     df <- data.frame(
>         spline(df[c("index", xname)], ...)$y,
>         spline(df[c("index", yname)], ...)$y
>     )
>     colnames(df) <- c(xname, yname)
>     return(df)
> }

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