I know I can do this
a <- dt[,sum(x), by=y ]
I can do this too
dt[,z:=sum(x), by=y] # this would modify dt
But I don’t know why I can’t do this:
a <- dt[,z=sum(x), by=y]
< p>How to perform "summarization" with custom column names?
Is this the only option?
a <- copy(dt)
a[,z:=sum(x), by=y]
You are looking for the list() in the j parameter:
a < -dt[,list(z=sum(x)), by=y]
I know I can do this
a <- dt[,sum(x), by=y]
I can do this too
dt [,z:=sum(x), by=y] # this would modify dt
But I don’t know why I can’t do this:
a <- dt[,z=sum(x), by=y]
How to perform "summarization" using custom column names?
Is this the only option?
a <- copy(dt)
a[,z:=sum(x), by=y]
You are looking for the list() in the j parameter:
a <- dt[,list(z=sum(x) ), by=y]