[R] help wrapping findInterval into a function

[Steve E.]

Dear R Community,

I hope you might be able to assist with a small problem creating a function. 
I am working with water-quality data sets that contain the concentration of
many different elements in water samples.  I need to assign quality-control
flags to values that fall into various concentration ranges.  Rather than a
web of nested if statements, I am employing the findInterval function to
identify values that need to be flagged and to assign the appropriate flag. 
The data consist of a sample identifier, the analysis, and corresponding
value.  The findInterval function works well; however, I would like to
incorporate it into a function so that I can run multiple findInterval
functions for many different water-quality analyses (and I have to do this
for many dataset) but it seems to fall apart when incorporated into a
function.

Run straighforward, the findInterval function works as desired, e.g. below,
creating the new CalciumFlag column with the appropriate flag for, in this
case, levels of calcium in the water:

WQdata$CalciumFlag <- with(WQdata, ifelse(analysis == "Calcium", (flags <-
c("Y", 'Q', "", "A") [findInterval(WQdata$value, c(-Inf, 0.027, 0.1, 100,
Inf))]),""))

However, it does not worked when wrapped in a function (no error messages
are thrown, it simply does not seem to do anything):

WQfunc <- function() {
	WQdata$CalciumFlag <- with(WQdata, ifelse(analysis == "Calcium", (flags <-
c("Y", 'Q', "", "A") [findInterval(WQdata$value, c(-Inf, 0.027, 0.1, 100,
Inf))]),""))
	}

Calling the function WQfunc() does not produce an error but also does not
produce the expected CalciumFlag, it seems to not do anything.

Ultimately, what I need to get to is something like below where multiple
findInterval functions for different analyses are included in a single
function, then I can concatenate the results into a single column containing
all flags for all analyses, e.g.:

WQfunc <- function() {
	WQdata$CalciumFlag <- with(WQdata, ifelse(analysis == "Calcium", (flags <-
c("Y", 'Q', "", "A") [findInterval(WQdata$value, c(-Inf, 0.027, 0.1, 100,
Inf))]),""))

	WQdata$SodiumFlag <- with(WQdata, ifelse(analysis == "Sodium", (flags <-
c("Y", 'Q', "", "A") [findInterval(WQdata$value, c(-Inf, 0.050, 0.125, 125,
Inf))]),""))

	WQdata$MagnesiumFlag <- with(WQdata, ifelse(analysis == "Magnesium", (flags
<- c("Y", 'Q', "", "A") [findInterval(WQdata$value, c(-Inf, 0.065, 0.15, 75,
Inf))]),""))
	
.....etc for additional water-quality analyses...

	}

As an aside, I started working with the findInterval tool from an example
that I found online but am not clear as to how the multi-component
configuration incorporating brackets actually works, can anyone suggest a
good resource that explains this?


I thank you very much for any assistance you may be able to provide.


Regards,
Steve

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