Hello -
Andrew Rominger wrote:
Dear list,
I'm afraid this is a mundane question. Here's the background: I've
produced a function which allows me to sequentially measure angles and
distances from a specified reference point to a curve defined by
empirical data points while (i.e. using a while loop) the angle being
measured is within certain bounds. Because the curve is circular I need
to pars the data into basically an "upper" curve and "lower" curve. I
tried to do this with an if statement, specifically:
ycrit<-subset(data,subset=data$x==min(data$x)
You might consider not using 'data' as a variable name (it is the name
of a function in the utils package) , and clearer code might be
ycrit <- subset(data, x == min(x))
But what does this return? It can definitely return a data.frame as in
the following example:
t1 <- data.frame(a = rep(2,2))
t1
class(subset(t1, a == min(a)))
You probably do not want to them subsequently use this returned subset
in an 'if' clause. Also, consider cases where there are NAs in the data:
t2 <- data.frame(a = c(NA,rep(2,2)))
t2
subset(t2, a == min(a))
This code returns a data.frame with 0 rows.
I don't know what your specific problem is, but hopefully this might
lead you in the right direction.
y.max<-length*sin(angle)+y.ref #length, angle and y.ref are given
if(y.max<ycrit){
........
}
Now the problem: The while loop works for 4 iterations, until I get the
error message:
"Error in if (y.max < ycrit) { : missing value where TRUE/FALSE needed"
When I forced the function to print y.max and ycrit for each iteration
of the while loop, it returns finite real numbers, including ycrit =
153.5 and y.max = 245.16 for the step which returns the error message.
Any ideas about what's going on here--why does R "think" that
245.16<153.5 is "missing," or is anything other than TRUE/FALSE? Am I
using "if" incorrectly? In which case would it be more appropriate to
perhaps create subsets of the data points based on < or > ycrit?
Thanks in advance for any guidance--
Andy
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