[R] using integrate on a function defined with if

[Faheem Mitha]

Dear R People,

I getting some curious behaviour with the integrate function. Consider the
function

foo <- function(x)
  {
    if(x==0)
	4
	else
	0
	}

I get the error

> integrate(foo,0,1)
Error in integrate(foo, 0, 1) : evaluation of function gave a result of
wrong length

But now consider

foo <- function(x)
  {
    ifelse(x==0,4,0)
  }

> integrate(foo,0,1)
0 with absolute error < 0

I am guessing this may have something to do with types/classes, but I
don't see exactly what. I would be happy to be enlightened.

Yhe help page says the function must be

"f An R function taking a numeric first argument and returning a numeric
vector the same length."

But I don't see any difference in what these two return. In both cases it
is NULL.

                                  Sincerely, Faheem Mitha.

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