NA Error min Function in R - r

Question

I am running into an error using R's min() function.
wip <- read.csv("WIP-01-11-11.csv") # Get WIP CSV
wip <- transform(wip, End.Date=as.Date(wip$End.Date,format='%d-%b-%y', na.rm=T))
wip <- transform(wip, Start.Date=as.Date(wip$Start.Date,format='%d-%b-%y', na.rm=T))
wip2 <- transform(wip, duration=ifelse(
round((wip3$End.Date - wip3$Start.Date)/30, digits = 0)==0,
1,
round((wip3$End.Date - wip3$Start.Date)/30, digits = 0)))
# At this point, I get NAs
wip3 <- transform(wip2, monthsRec=min( (
(2011*12+11) - as.numeric(format(wip3$Start.Date, '%Y'))*12 +
as.numeric(format(wip3$Start.Date, '%m'))),
wip3$duration)
)
Why am I getting NAs in the "duration" calculation for wip2 when End.Date and Start.Date have no NAs.
Thanks,

Answer 1

wip3 = list()
wip3$Start.Date = as.Date('2011-01-01')
wip3$duration = 10
> min(((2011*12+11) - as.numeric(format(wip3$Start.Date, '%Y'))*12+as.numeric(format(wip3$Start.Date, '%m'))),wip3$duration)
[1] 10
Works fine for me. Do you have any NAs in your data? If so, you probably want to use the na.rm=T flag to min().

Answer 2

I reproduced your problem with #John Colbys example if I use the wrong casing for wip3$start.Date:
wip3 = list()
wip3$start.Date = as.Date('2011-01-01')
wip3$duration = 10
min(((2011*12+11) - as.numeric(format(wip3$Start.Date, '%Y'))*12+as.numeric(format(wip3$Start.Date, '%m'))),wip3$duration)
Which produces
[1] NA
Warning messages:
1: NAs introduced by coercion
2: NAs introduced by coercion
I suspected since you have wip3$duration, you probably have wip3$start.Date too - but you accessed it as wip3$Start.Date in your code. That returns NULL, which doesn't work well with the rest...