R help - Oct 2015 - Replace NaN from 1 column with a value from the same row

Hi everyone,
Ignore my previous post, i realised that the rows and columns i typed into the
email were unreadable, sincere apologies for this.
A simple question, but i cannot figure this out.
I have a data-frame with 4 columns (onset, offset, outcome, mean):
df<-data.frame(onset=c(72071,142598,293729), offset=c(72503,143030,294161),
outcome=c(1,1,1), mean=c(7244615,NaN,294080))
For each 'NaN' in the mean column, i want to replace that NaN with the
'offset' value in the same row. I tried:
df$mean <- replace(df$mean, is.na(df$mean), df$offset)
but i get the error message: 'number of items to replace is not a multiple
of replacement length'. I'm assuming because this is trying to insert
the whole 'offset' column into my one NaN cell. Is this a correct
interpretation of the error message?
Can anyone tell me how to replace any mean row NaN's with the offset value
from that very same row?I don't want to use any pasting etc as this needs to
be used as part of a function working over a larger data set than the one shown
here.
CheersJonathan  		 	   		  
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