[R] conditional replacement of character strings in vectors

[David Winsemius]

On Sep 2, 2011, at 7:51 PM, R. Michael Weylandt wrote:

> Your data frame didn't come across legibly, try sending it in plain  
> text
> using the dput() command.
>
> That said, I'd guess you want something like this:
>
> d[is.na(d$a),"a"] <- d[is.na(d$b),"b"]

One of the rare instances where I disagree with Michael. The row index  
on the right hand side must be the same as the row index on the left  
hand side.

>
> The idea is that is.na(d$a) selects only those rows where column "a"  
> is NA
> and then moves b values into a for only those rows.

Right, that is the idea.

>
> Write back with the dput() data frame if this doesn't work.
>
> Hope this helps,
>
> Michael Weylandt
>
> On Fri, Sep 2, 2011 at 3:51 PM, Josh Tewksbury <tewksjj at uw.edu> wrote:
>
>> Hello, I have a dataframe that looks like this:
>>
>> a b  NA Honduras  China NA  NA Sudan  Japan NA  NA Mexico  NA Mexico
>> I would like to replace the NA values in column b with the non-NA  
>> values in
>> column a.  I have tried a number of techniques, (if, ifelse) but I  
>> must
>> have
>> the logic wrong.
>>
>> Thanks
>> --
>> Josh

David Winsemius, MD
West Hartford, CT