Debugging only when needed
One of the worst thing I experienced is having a bug in a nested call of functions. If it is not simple the problems comes to isolate when and why does it occur. Here I explore something that I found once on twitter but haven’t find explained in Advanced R or other blogs.
Function stack
A simple function to debug is this one:
myfunction1 <- function(x, y) {
if (sum(x > 0) >= 5) {
x + y
} else {
x - y
}
}We can use it:
myfunction1(runif(10), 5)
## [1] 5.703426 5.516683 5.217670 5.943402 5.173702 5.137270 5.768233 5.132304
## [9] 5.513719 5.404423
myfunction1(runif(4), 5)
## [1] -4.706239 -4.447211 -4.078848 -4.997719However if our input has a NA we’ll get an error:
x <- runif(10)
x[5] <- NA
myfunction1(x, 5)
## Error in if (sum(x > 0) >= 5) {: missing value where TRUE/FALSE neededThe problem is easy to find but lets assume it is not.
The missing value where TRUE/FALSE needed indicates that we get a NA.
So to find where we can use browser and the expression argument as this:
myfunction2 <- function(x, y) {
browser(expr = any(is.na(x)))
if (sum(x > 0) >= 5) {
x + y
} else {
x - y
}
}
myfunction2(x, 5)Which lead us to this:
debug with expr
If we use other input we can use the function as usual without triggering the debug:
myfunction2(runif(6), 5)
## [1] 5.231687 5.008704 5.614821 5.561843 5.745173 5.026838So if you are developing a package or functions and find an error on some calculation and you don’t want to press next or skip a loop just use the expr argument of browser to just jump into the problematic call.
Reproducibility
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## date 2021-01-08
##
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