Question

I would like to address the rows of a data frame by a string name, and the table will be built sequentially. I want to do something like

> mytab <- data.frame(city=c("tokyo","delhi","lima"),price=c(9,8,7),row.names=1)
> mytab
      price
tokyo     9
delhi     8
lima      7 
> # I can add a new row
> mytab["london",] = 8.5

I now need to check whether a row name already exists.

> mytab["ny",]
[1] NA

Is there anything better that I can do other than

> if (is.na(mytab["ny",])) { mytab["ny",]=9;}

since a NA may possibly arise otherwise?

Answer 1

Something like this

if (!('ny' %in% row.names(mytab))) {mytab['ny',]=9}

might do the trick.