Thought #1 -- Consistency
----------
Quick thought -- would it be more consistent if the interface took in the name
of the variable directly rather than a string?
In other words, would
dt[,a] <- "b"
be more consistent with the existing data.table interface than
dt[,"a"] <- "b"
?
Then again, taking in a string of the column name avoids the temptation to
having complex expressions (like a+23*c) as the name of the column. Although I
just argued against my own point, I am curious what other people think.
Thought #2 -- Alternative interfaces suggested in past
----------
Also, there were some other messages in the past discussing having an interface
similar to:
dt[,{a = "b"}]
dt[,{T(temp_a) = "b"; a = temp_a}]
etc.
What are the merits of having the ability to set values integrated into the
"[.data.table" function?
Regards,
Harish
--- On Mon, 8/2/10, Short, Tom <[email protected]> wrote:
> From: Short, Tom <[email protected]>
> Subject: Re: [datatable-help] Wonder whether there is an easier way to
> changepart of data.table values
> To: "Branson Owen" <[email protected]>,
> [email protected]
> Date: Monday, August 2, 2010, 7:28 PM
> I've just checked in versions of
> [<-.data.table and $<-.data.table that
> check for the columns adjusted and reset the key if
> appropriate. This
> brings up some incompatibilities:
>
> (*) KEYS -- Before, you could do:
>
> dt$key_column = anything
>
> And it wouldn't change the status of the key. Now, the key
> will be
> nullified.
>
> (*) ASSIGNMENT DIFFERENCE
>
> Before: dt["a"] <- "b" meant change column a.
> Now: dt[,"a"] <- "b"
>
> Now, you can do
> dt[J("a"), "somecol"] <- 33 means assign 33 to the
> column "somecol"
> based on the key being equal to "a".
>
> (*) QUESTIONS
>
> - Do we need a "keep.key" argument for cases where we don't
> want the key
> nullified (the user knows the order is unaffected). This
> isn't really
> possible for dt$a[1:4] <- something.
>
> - Is it a good idea to use data.table-style indexing for
> the i part of
> [<-.data.table? I was skeptical when Branson first asked
> (prefering
> data.frame compatibility), but it makes more sense now that
> I think
> about it.
>
> Finally, we should put a warning in the documentation
> somewhere that
> functions that re-arrange or assign values to a data frame
> may "corrupt"
> the key of a data.table. Data.table-aware functions should
> account for
> this, but other functions may not.
>
> - Tom
>
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