dot list alias doesn't work with between

[Henrik-P]

From ?between:

X = data.table(a = 1:5, b = 6:10, c = c(5:1)) 
X[c %between% list(a, b)]

list can't be replaced by .( ) here:

X[c %between% .(a, b)]
# Error in .(a, b) : could not find function "."

[MichaelChirico]

I think . is only interpreted in the j clause, and when it's the only thing in i... you're right that this probably deserves explication in a help page, perhaps we should add an Rd for ?"."

…

On Aug 21, 2017 8:21 PM, "Henrik-P" ***@***.***> wrote: From ?between: X = data.table(a = 1:5, b = 6:10, c = c(5:1)) X[c %between% list(a, b)] list can't be replaced by .( ) here: X[c %between% .(a, b)] # Error in .(a, b) : could not find function "." No big deal, but I just wonder if this is expected? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2315>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AHQQdYNlkKwM0zNY8aJRkavubnrBy687ks5sahD3gaJpZM4O97zH> .

[franknarf1]

@MichaelChirico Of course, it's available in the i, on and by clauses as well. I kind of expect it to work throughout i and j, no matter the form of the expression, anyways. I have a somewhat related SO post https://stackoverflow.com/questions/41228076/using-data-tables-shortcut-in-quoted-expressions

[MichaelChirico]

speaking off the cuff here, you're more correct. and i agree it'd be nice to have everywhere

…

On Aug 21, 2017 8:32 PM, "Frank" ***@***.***> wrote: @MichaelChirico <https://github.com/michaelchirico> Of course, it's available in the i, on and by clauses as well. I kind of expect it to work throughout i and j, no matter the form of the expression, anyways. I have a somewhat related SO post https://stackoverflow.com/ questions/41228076/using-data-tables-shortcut-in-quoted-expressions — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#2315 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AHQQdfAydyx5YkKRPob4_rx5-O057i_Oks5sahOggaJpZM4O97zH> .

[Henrik-P]

Just to provide a small background if considering an update of the help text and/or usage of .()

Currently, .( ) is (more or less) explicitly described in:

• Explicit in the Arguments section of j:

"The expression .() is a shorthand alias to list()")

• Slightly less explicit in the Arguments section of by:

a list() of expressions of column names: e.g., DT[, .(sa=sum(a)), by=.(x=x>0, y)]

• Slightly less explicit in the Arguments section of on:

also possible to use .() syntax as X[Y, on=.(a, b)]

• First j Examples

DT[, .(v)] # same as above, .() is a shorthand alias to list()

• Quite far down among the i Examples

kDT[.("a")] # same, .() is an alias for list()

Some thoughts:

1. Given the frequent use of .() in i, and to make the help text more consistent, I think .() could be mentioned explicitly also in the Arguments section of i.
2. In the i Examples, it would be better to describe .( ) when it first occurs (DT[.("a"), on="x"]).
3. Either describe exceptions to when .() works (like e.g. my between and in Frank's SO post) or, as Frank wrote, make it work throughout i and j.