Dear useRs,
Just a little post to provide the answer of a problem that took me
some time to resolve !
Hope that reading this will permit the others to avoid that error.
When using the subset function, writing
subset (data, data$columnname == X) or subset (data, columnname == X)
do the same thing.
thus, the function consider that argument name given after the coma
(like "columnname") is the name of a column of the data frame
considered.
A problem occur when other arguments such as X are the names of both a
column of the data frame and an object !
Here is an example:
df <- data.frame(ID = c("a","b","c","b","e"), Other = 1:5)
ID <- unique (df$ID)
ID
## Now the potential problem !!
subset (df, df$ID == ID[4])
## BE CAREFUL subset function use the column ID of the data.frame
## and NOT the object ID containing unique value !!!!
Sorry if it seems obvious for some of you, but hope that others find
it useful !!
Arnaud
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