[R] else problem

[Bert Gunter]

Perhaps some additional clarification...  (???)

>> 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 {
>
> If this line is executed at a console session it will fail because the
> interpreter does not keep a copy of the last condition. If you moved the
> closing curley-brace to just befor the 'else', you should get the behavior
> you expect (if your other code is correct):

Well, um.. not sure if this is what you meant, but what is happening
at the console is that when you type <return>, the interpreter checks
for a syntactically complete statement. If it finds what has been
given to it **thus far** is, it tries to execute it (if not, it gives
a continuation character and waits for more input) and, as you said,
then starts anew to interpret the next line(s) entered, "forgetting"
all previous. The problem above is that the" if()" statement up to the
close bracket, "}" is syntactically complete, and so the "else{" that
follows makes no sense as the beginnig of a new line to  be
interpreted.

The simplest and universal solution to this is to simply enclose the
whole conditional in" { }":

{if(length ...
...
else {...}
}

This forces the interpreter to wait for the last "}" before it will
interpret and execute.

Hoping this clarifies rather than obfuscates.

-- Bert



>
> Try instead:
>
> if (length(dat2f$year)%%2==0) {
>  md <-dat2f[, list(med_year = max(year[which(abs(tot_km3y -
> median(tot_km3y)) == min(abs(tot_km3y - median(tot_km3y)))) ]), med_TotQ =
> median(tot_km3y))]
> } else {
>  md <-dat2f[, list(med_year = year[which(tot_km3y == median(tot_km3y))],
> med_TotQ = median(tot_km3y))]
>  }
>
>
>>  md <-dat2f[, list(med_year = year[which(tot_km3y == median(tot_km3y))],
>> med_TotQ = median(tot_km3y))]
>>  }
>>
>> Each individual piece works perfectly on its own, but together I get the
>> following error:
>>
>>> if (length(dat2f$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"
>
> Try instead:
>
> ?"else"
>
> --
> David
>>
>> 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
>
> David Winsemius, MD
> West Hartford, CT
>
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>



-- 
"Men by nature long to get on to the ultimate truths, and will often
be impatient with elementary studies or fight shy of them. If it were
possible to reach the ultimate truths without the elementary studies
usually prefixed to them, these would not be preparatory studies but
superfluous diversions."

-- Maimonides (1135-1204)

Bert Gunter
Genentech Nonclinical Biostatistics