Give suggestions for vector->row vector confusion

[ivarne]

Some new users might get confused when they create a vector without
commas, and end up with a matrix that does not match the methods he
tries to use. After this patch the error will contain a suggestion.

julia> a = [1 2 3]
1x3 Array{Int64,2}:
 1  2  3

julia> sort(a)
ERROR: `sort` has no method matching sort(::Array{Int64,2})

You might have used a 2d row vector where a 1d column vector was required.
Note the difference between 1d column vector [1,2,3] and 2d row vector [1 2 3]
You can convert a row vector to a column vector with the vec() function

See: https://groups.google.com/forum/#!topic/julia-users/XBjl1sPfTkU and #7512

Suggestions for better wording/formatting is most welcome.

[jiahao]

+1

[porterjamesj]

I was very confused by this when I was learning, + a lot

[ViralBShah]

I like the idea of giving a clear message.

[ivarne]

The build failure seems unrelated (even though it seems scary that it is the repl.jl tests that is failing).

[Keno]

Maybe point to the vec function?

[ivarne]

Does anyone have any objections against this, or should I just squash and merge?

[timholy]

Nice implementation. One small nit: it might be better to say you can convert Arrays to a vector using vec (the current statement seems to suggest vec is more limited than that).

[ViralBShah]

I think it should be ok to squash and merge.

[ivarne]

I don't think it suggests vec is limited to row vectors.

I think it is more important to stress the type difference between row and column vectors in Julia, than to provide a complete description of what vec can be used for. The help text will only be displayed when you get a MethodError for using a row vector where a column vector would have worked.

[timholy]

I agree that the clarification of row vs column (and space vs comma) much needed---this comes up over and over, and it will be great to have this fixed in such a good, general way.

I was just suggesting converting You can convert a row vector to a column vector with the vec() function to something like You can convert to a column vector with the vec function. But this is a tiny point, and the benefits awaiting users from the merger of this PR should not be delayed any longer! 😄

[ivarne]

Yes, that seems better. I did not like the reference to Array in the first suggestion.

[ivarne]

Wrong button 😠

[timholy]

Looks like this version omitted the mention of vec.

[timholy]

Never mind, this was a wait-for-GitHub-to-update issue.

[ivarne]

Sorry, somehow git happily does a git commit --amend without requiring me to to add anything first (supposedly to change the commit message, which I did). I pushed a new correct commit a few minutes later.