如何捕捉“需要至少两个非NA值插值”

Question

从Find x-intercept and y-intercept of a loop in R我得到了这个很好的解决方案。但它崩溃，如果在这个例子当然没有像拦截：

x <- sin(seq(0,2*pi,0.2) + rnorm(1)) 
y <- cos(seq(0,2*pi,0.2) + rnorm(1)) 

intercepts(x,y+10) 


intercepts <- function(x,y) { 
    x.s <- approxfun(x[y<=0], y[y<=0])(0) 
    x.n <- approxfun(x[y>=0], y[y>=0])(0) 
    y.w <- approxfun(y[x<=0], x[x<=0])(0) 
    y.e <- approxfun(y[x>=0], x[x>=0])(0) 

    list(x.s, x.n, y.w, y.e) 
} 

我怎样才能防止碰撞的功能，并返回NA小号如果没有拦截可寻？

我试过到目前为止：

getIntercept <- function(x,y) { 

    xydf <- data.frame(x,y) 
    xy.n <- subset(xydf,y>=0) 
    xy.s <- subset(xydf,y<=0) 
    xy.e <- subset(xydf,x>=0) 
    xy.w <- subset(xydf,x<=0) 

    if ((length(xy.n$y) * length(xy.s$y) >=1) & (length(xy.e$y) * length(xy.w$y) >=1)) { 
    ## interception in north and south 
    Ra <- approxfun(xy.n$x,xy.n$y)(0) 
    Rb <- approxfun(xy.s$x, xy.s$y)(0) 

    ## interception in east and west 
    Ca <- approxfun(xy.e$x,xy.e$y)(0) 
    Cb <- approxfun(xy.w$x,xy.w$y)(0) 
    return(data.frame(Ra,Rb,Ca,Cb, 
         Rmean=mean(Ra,-Rb), Rerr=(Ra+Rb)/2, 
         Cmean=mean(Ca,-Cb), Cerr=(Ca+Cb)/2)) 
    } else { return(data.frame(Ra=0,Rb=0,Ca=0,Cb=0, Rmean=0, Rerr=0, Cmean=0, Cerr=0)); } 
} 

Answer 1

简单的解决方案，在任何错误的情况下返回NA：

intercepts <- function(x,y) { 
    x.s <- tryCatch(approxfun(x[y<=0], y[y<=0])(0), error=function(e) NA) 
    x.n <- tryCatch(approxfun(x[y>=0], y[y>=0])(0), error=function(e) NA) 
    y.w <- tryCatch(approxfun(y[x<=0], x[x<=0])(0), error=function(e) NA) 
    y.e <- tryCatch(approxfun(y[x>=0], x[x>=0])(0), error=function(e) NA) 

    list(x.s, x.n, y.w, y.e) 
}