[R] filling area under a function line

[Tom H]

Hi R collective,

I quite like the "curve" function because you can chuck a R function
into it, and see the graph in one line of R.

I had a google and found some threads for filling under the line;
http://tolstoy.newcastle.edu.au/R/e2/help/07/09/25457.html

However they seem to miss the point of the simplicity of going, "I
wonder what that looks like, and can I have some colour with that
please ;-)" 

So I found the easiest way to do that was to attach a polygon call onto
the end of the curve function definition;

        else plot(x, y, type = type, ylab = ylab, xlim = xlim, log = lg, 

+       polygon(
+                       c(from,  x, to), 
+                       c(min(y),y,min(y)),
+                       col=areacol, lty=0
+       )

}

areacurve(sin(2*pi*6*x+pi/2),areacol="red")

and stick that in my r init file. 

Now the question is, am I missing something elementary here?

Cheers,

T







areacurve<-function (expr, from = NULL, to = NULL, n = 101, add =
FALSE, 
                type = "l", ylab = NULL, log = NULL, xlim = NULL,
areacol="gray", ...) 
{
        sexpr <- substitute(expr)
        if (is.name(sexpr)) {
                fcall <- paste(sexpr, "(x)")
                expr <- parse(text = fcall)
                if (is.null(ylab)) 
                        ylab <- fcall
        }
        else {
                if (!(is.call(sexpr) && match("x", all.vars(sexpr), nomatch = 
0L))) 
                        stop("'expr' must be a function or an expression 
containing 'x'")
                expr <- sexpr
                if (is.null(ylab)) 
                        ylab <- deparse(sexpr)
        }
        if (is.null(xlim)) 
                delayedAssign("lims", {
                                        pu <- par("usr")[1L:2]
                                        if (par("xaxs") == "r") 
                                                pu <- extendrange(pu, f = -1/27)
                                        if (par("xlog")) 
                                                10^pu
                                        else pu
                                })
        else lims <- xlim
        if (is.null(from)) 
                from <- lims[1L]
        if (is.null(to)) 
                to <- lims[2L]
        lg <- if (length(log)) 
                                log
                        else paste(if (add && par("xlog")) 
                                                        "x", if (add && 
par("ylog")) 
                                                        "y", sep = "")
        if (length(lg) == 0) 
                lg <- ""
        x <- if (lg != "" && "x" %in% strsplit(lg, NULL)[[1L]]) {
                                if (any(c(from, to) <= 0)) 
                                        stop("'from' and 'to' must be > 0 with 
log=\"x\"")
                                exp(seq.int(log(from), log(to), length.out = n))
                        }
                        else seq.int(from, to, length.out = n)
        y <- eval(expr, envir = list(x = x), enclos = parent.frame())


        if (add) {
                lines(x, y, type = type, ...)
        }
        else plot(x, y, type = type, ylab = ylab, xlim = xlim, log = lg, 
                                ...)

        polygon(
                        c(from,  x, to), 
                        c(min(y),y,min(y)),
                        col=areacol, lty=0
        )
        
}

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