[FR] gather_all / gather 'smart' default when only key and value given

[npjc]

example data

df <- structure(list(d = c(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1), l1 = c(1.5, 
1.5, 1.5, 1.5, 1.5, 1.5, 2, 2, 2, 2, 2, 2), l2 = c(1.83333333333333, 
1.83333333333333, 2.16666666666667, 2.16666666666667, 2.5, 2.5, 
2.33333333333333, 2.33333333333333, 2.66666666666667, 2.66666666666667, 
3, 3), l3 = c(2.33333333333333, 2.83333333333333, 2.66666666666667, 
3.16666666666667, 3, 3.5, 2.83333333333333, 3.33333333333333, 
3.16666666666667, 3.66666666666667, 3.5, 4)), class = "data.frame", row.names = c(NA, 
-12L), .Names = c("d", "l1", "l2", "l3"))

head(df)

    d  l1       l2       l3
1   1 1.5 1.833333 2.333333
2   1 1.5 1.833333 2.833333
3   1 1.5 2.166667 2.666667
4   1 1.5 2.166667 3.166667
5   1 1.5 2.500000 3.000000
6   1 1.5 2.500000 3.500000

intention

gather all columns of df into x,y.

current UI

df %>% gather(x, y, d:l3)

request

It would be nice if gather had an all-inclusive default when only key and value arguments are provided. This seems like the most intuitive default to me as I don't think you'd ever want to gather
no columns into a key and value... This would mean that for df the following "smart default" would be equivalent to the current UI (gather all columns).

df %>% gather(x, y)

the select() philosophy

Would this be confusing? Does it go against select()?

Now I think this impacts the whole opposite to the select() paradigm. That is if ... is NULL it current selects nothing... but what is the use case for selecting nothing? There are definitely some use cases for selecting everything ( such as that within gather() ).

In the quest of making code more naturally reader friendly an empty selection giving everything is definitely a negative... so perhaps an alternative solution:

df %>% gather(x, y, all= TRUE)
df %>% gather_all_into(x, y)
df %>% gather_into(x, y)  # think: spread_outof(x,y) to reverse?

but my favorite...

df %>% into(x, y) # opens the door to 'outfrom()` / `outof`

[rpruim]

I was going to post a similar thing wondering if gather() could gather all columns when ... is empty.

[hadley]

This seems reasonable to me.