```
DT = data.table(a=seq(0,1,by=0.2),b=1:2, key="a")
DT
setNumericRounding(0) # By default, rounding is turned off
DT[.(0.4)] # works
DT[.(0.6)] # no match, can be confusing since 0.6 is clearly there in DT
# happens due to floating point representation limitations
setNumericRounding(2) # round off last 2 bytes
DT[.(0.6)] # works
# using type 'numeric' for integers > 2^31 (typically ids)
DT = data.table(id = c(1234567890123, 1234567890124, 1234567890125), val=1:3)
print(DT, digits=15)
DT[,.N,by=id] # 1 row, (last 2 bytes rounded)
setNumericRounding(0)
DT[,.N,by=id] # 3 rows, (no rounding, default)
# better to use bit64::integer64 for such ids
```

Run the code above in your browser using DataLab