[datatable-help] aggregating data

[David Bellot]

Hi,

I have a data.table DT with one of the column named x and I other names,
let's say, a1, a2, ... aN. The key of this data.table is made of a1...aN.

Later on, I aggregate my DT with x like this:
agg = DT[ , list(m=mean(y), c=length(y)), by = c("x") ]

The problem is that "x" has 331 unique values as found by
length(unique(DT$x)) but my result "agg" only has 119 rows. I tried by
changing the key to "x" alone but the problem persists. My DT table has a
few millions rows by the way.

I'm sure I'm missing something totally obvious :-( !!!!

Any idea ?

Best,
David
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