[R] help wrapping findInterval into a function

[David Winsemius]

On Dec 6, 2011, at 11:43 AM, Steve E. wrote:

> 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.

It's probably your use of "with" rather than findInterval. The 'with'  
function sets up an environment and is used mostly in interactive  
session. If you have not passed a dataframe into the function then you  
should use the name of the dataframe and '['.


> 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
>
> --
> View this message in context: http://r.789695.n4.nabble.com/help-wrapping-findInterval-into-a-function-tp4165464p4165464.html
> Sent from the R help mailing list archive at Nabble.com.
>
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David Winsemius, MD
West Hartford, CT