feature request: automatically convert 1x1 matrix to a scaler number in proper cases

[wenxgwen]

It will be more convenient that Julia can automatically convert 1x1 matrix to a scaler number in proper cases.

The julia session :

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  | | |_| | | | (_| |  |  Version 0.2.0-rc2-prerelease+4331
 _/ |\__'_|_|_|\__'_|  |  Commit 902b446 2013-10-29 23:03:55 UTC
|__/                   |  i686-linux-gnu

julia> reload("test1")
ERROR: no method convert(Type{Float64},Array{Int32,1})
 in setindex! at array.jl:413
 in include at boot.jl:238
 in include_from_node1 at loading.jl:114
 in reload_path at loading.jl:140
 in reload at loading.jl:73
at /home/wen/Dropbox/prog/julia/STK/test1.jl:9

julia> 

The Julia code test1.jl:

K=[1 0; 0 2]

T=zeros(Float64,2,2)

l=[1; 1]
# The following works:  
T[2,2] =(l'*K*l)[1,1]
# The following does not work
T[1,1] =(l'*K*l)

# (l'*K*l) is a 1x1 Array, and Julia cannot treat it as a scaler number

A general and uniform way to handle this and other issues is to allow automatic (type?) conversion (when needed)
between array of size (n), (n,1), (n,1,1),(n,1,1,1) etc
(Just like we automatically convert real number to complex number when needed)

Xiao-Gang

[jiahao: edit for formatting. Please escape code with triple backquotes (```) so that Github formats it correctly]

[jiahao]

Related discussions: #3262 #4270 #2591 #2686

[ViralBShah]

This is something that we have taken a measured decision on, as @jiahao 's link to related discussions shows.

[StefanKarpinski]

Actually, this is a little different since it really has nothing to do with other indexing and vector, matrix, tensor behaviors. Assigning any single-element array into a scalar location in another array should probably just work.

[ViralBShah]

Would we want to treat single-element array assignments into an array location differently from other array assignments into an array location? What if the assignment is into Array{Any} on the left, where one may actually want the single element array assigned, rather than the scalar?

[JeffBezanson]

As has been discussed in those other issues, what we would do is allow
conversion to a lower-dimensional thing if trailing dimensions are 1.
On Nov 13, 2013 11:59 AM, "Viral B. Shah" [email protected] wrote:

Would we want to treat single-element array assignments from other array
assignments? What if the assignment is into Array{Any}, where one may
actually want the single element array assigned?

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