Find the index of minimum in a vector of vectors of vectors

New to Julia
1

I think my problem is fairly simple.

a = [[1,2], [3,4,5], 10]
b = [[2,3], [4,5,6], 1] 
c = [a,b]

I want to find the index where the last element is the smallest. In the example, the value is 1, and it should return 2.

I tried to use the “findmin()”, but I simply didn’t know how to access the last element of each row.

Is only “for” possible to achieve this?

2

Can’t you use the keyword by=last ? Check the documentation of findmin for the correct syntax.

2 Likes
3

Thank you very much for your reply. What if I wanted to collect only the last elements from “c”?

4

You request is unclear. There is also argmin that you may be able to use.

1 Like
5

The way I’ve thought is as follows

# collect only the last element of each row of the vector c. 

collection = Any[]

for (i,element) in enumerate(c)
push!(collection,element)
end

# find the index where the last element is the smallest 
ind = findmin(collection)

# return the row of c that contains the smallest last element
c[ind]
6

Try findmin(c,by=last)

You may also try broadcasting as collection=last.(c)

1 Like
7

findmin doesn’t seem to support a by keyword. The syntax for that seems to be findmin(last, c).

3 Likes
8

Just in case someone finds this thread helpful, I tried both.
Thank you so much everyone for the suggestions!

a = [[1,2], [3,4,5], 10]

b = [[2,3], [4,5,6], 1]

c = [a,b]

findmin(last,c)

(1, 2)

a = [1, [1,2], [3,4,5], 10]
b = [2, [3,3], [1,1,1], 20]

c= [a,b]

findmin(c,by=last)

MethodError: no method matching findmin(::Vector{Vector{Any}}; by=last)
Closest candidates are:
  findmin(::AbstractArray; dims) at reducedim.jl:1112 got unsupported keyword argument "by"
  findmin(::Any) at reduce.jl:977 got unsupported keyword argument "by"
  findmin(::Any, !Matched::SparseArrays.AbstractSparseVector{T}) where T at /Applications/Julia-1.8.5.app/Contents/Resources/julia/share/julia/stdlib/v1.8/SparseArrays/src/sparsevector.jl:1432 got unsupported keyword argument "by"
  ...

Stacktrace:
 [1] kwerr(::NamedTuple{(:by,), Tuple{typeof(last)}}, ::Function, ::Vector{Vector{Any}})
   @ Base ./error.jl:165
 [2] top-level scope
   @ ~/Documents/Migration/Julia Code/Quantitative (simple)/W SMM BF (March 4).ipynb:6