[R] conditional data replace (recode, change or whatsoever)

[Justin]

zcatav <zcatav <at> gmail.com> writes:

> 
> Your suggestion works perfect as i pointed previous message. Now have another
> question about data editing. I try this code:
> X[X[,"c"]==1,"b"]<-X[,"d"]
> and results with error: `[<-.data.frame`(`*tmp*`, X[, "c"] == 1, "b", value
> = c(NA,  : 
>   replacement has 9 rows, data has 2
> 

is this equivalent and/or preferred to:

X$b[X$c==1]<-X$d[X$c==1] ??

I assume this goes back to the various indexing methods for a dataframe, an
object vector that is a column of a data frame vs. an object data frame that
happens to be one column of a larger data frame.

on a very large data set is one preferable for speed?  one for memory use?

I tend to index using $ operators often and if I should quit let me know!!


Thanks,

Justin

> Logically i selected 2 rows with X[,"c"]==1. Than i want to replace in that
> rows its own data from "d" to "b" with X[,"b"]<-X[,"d"]. What is wrong?
> 
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