[R] else problem

[Kara Przeczek]

Dear R users,
I have run into a problem using if...else and I hope you can shed some light on it. I am using R version 2.2.0.1.

I have the following data frame:
> head(dat2f)
     year  tot_km3y
[1,] 1964 0.1876854
[2,] 1965 0.1835116
[3,] 1966 0.1915012
[4,] 1967 0.1869758
[5,] 1968 0.2249865
[6,] 1969 0.1916011

I need to pick out the median year, and since there are an even number of data, I cannot use 'median' directly since it gives me a non-existent year/discharge. I found a way to get around that with the following:

  md <- dat2f[, list(med_year = max(year[which(abs(tot_km3y - median(tot_km3y)) == min(abs(tot_km3y - median(tot_km3y)))) ]), med_TotQ = median(tot_km3y))]
(I really only need the year, not the actual discharge with that year, which is why I left med_TotQ as the true median)

However, I have some data sets that have an odd number of data for which the following works perfectly:

  md <-dat2f[, list(med_year = year[which(tot_km3y == median(tot_km3y))], med_TotQ = median(tot_km3y))]

Thus, I would like to apply the above calculations depended on the condition of:

length(dat2f$year)%%2==0

I put it all together as below:

if (length(dat2f$year)%%2==0) {
  md <-dat2f[, list(med_year = max(year[which(abs(tot_km3y - median(tot_km3y)) == min(abs(tot_km3y - median(tot_km3y)))) ]), med_TotQ = median(tot_km3y))]  }
else {
  md <-dat2f[, list(med_year = year[which(tot_km3y == median(tot_km3y))], med_TotQ = median(tot_km3y))]
  }

Each individual piece works perfectly on its own, but together I get the following error:

> if (length(dat2f$year)%%2==0) {
+   md <-dat2f[, list(med_year = max(year[which(abs(tot_km3y - median(tot_km3y)) == min(abs(tot_km3y - median(tot_km3y)))) ]), med_TotQ = median(tot_km3y))] }
> else {
Error: unexpected 'else' in "else"
>   md <-dat2f[, list(med_year = year[which(tot_km3y == median(tot_km3y))], med_TotQ = median(tot_km3y))]
>   }
Error: unexpected '}' in "  }"
>

When I tried to look up "else" I got this error:

> ?else
Error: unexpected 'else' in "?else"

I have used exactly the same set up with if...else in other code and it worked fine then. I tried to run it again, and I got the same error as above. What is the problem? I hope it isn't something simple and silly!

I realize that I can use the first line:

  md <- dat2f[, list(med_year = max(year[which(abs(tot_km3y - median(tot_km3y)) == min(abs(tot_km3y - median(tot_km3y)))) ]), med_TotQ = median(tot_km3y))]

for all data sets and it will give me the median for both odd and even-length data sets, but it is now about the principle; why won't the if...else work?

Thank you very much for your time!

Kara