A couple tuple questions

[yaois...@gmail.com]

Hi all,

I thought to just add to my previous thread, but created a new one because the topic is a bit different. Hope y'all don't mind.

Anyhow:

a) How would I concatenate two tuples? Or a tuple with a variable?

Say I have

testtuple = (1,2,3)
testvar = 4

and want to get

newtuple = (1,2,3,4)

(not ((1,2,3),4)

I've tried

newtuple = tuple(testtuple...,testvar...)
newtuple = tuple(testtuple...,testvar)
newtuple = testtuple...,testvar

but none of those have worked to produce the desired result.

b) I have an array of tuples

tuplearray = [(a1,b1,c1),(a2,b2,c2)...,(an,bn,cn)]

How could I then unpack the array into

aarray = [a1,a2...,an]
barray = [b1,b2...,bn]
carray = [c1,c3...,cn]

such that each position in the tuple gets unpacked into a corresponding individual array?

In Python, I would use

alist,blist,clist = zip(*tuplelist)

It appears that

aarray,barray,carray = zip(tuplearray...)

is not the Julia equivalent.

My version of Julia is the .3 RC.

Thanks for your help

[Leah Hanson]

a) Your second option works for me:

~~~

julia> testtuple = (1,2,3)

(1,2,3)

julia> testvar = 4

4

julia> tuple(testtuple...,testvar)

(1,2,3,4)

~~~

b) I'm not sure what the cleanest code for your example would be, but here's one possibility:

~~~

julia> tuplearray = [(1,2,3),(10,20,30),(100,200,300)]

3-element Array{(Int64,Int64,Int64),1}:

 (1,2,3)      

 (10,20,30)   

 (100,200,300)

julia> aarray = Int[]

0-element Array{Int64,1}

julia> barray = Int[]

0-element Array{Int64,1}

julia> carray = Int[]

0-element Array{Int64,1}

julia> for (a,b,c) in tuplearray

         push!(aarray,a)

         push!(barray,b)

         push!(carray,c)

       end

julia> aarray

3-element Array{Int64,1}:

   1

  10

 100

julia> barray

3-element Array{Int64,1}:

   2

  20

 200

julia> carray

3-element Array{Int64,1}:

   3

  30

 300

~~~

If would be faster to pre-allocate the arrays (to the length of the tuplearray), and then just put the elements in at the correct indices, but I'm not sure if that matters for your application.

-- Leah

[yaois...@gmail.com]

Leah, thanks for your detailed response --

I will take your advice and try to rework the code to pre-allocate for b).

In regards to a), I keep on getting the error message with the second option

ERROR: type: apply: expected Function, got (Int64,Int64,Int64) 

Just making sure, are you using 0.3? If so, hmm, I would be a bit stumped as to why the same line is not working for me.

[Kevin Squire]

Hi there,

In regards to a), I keep on getting the error message with the second option

ERROR: type: apply: expected Function, got (Int64,Int64,Int64) 

I'm guessing you accidentally redefined the symbol "tuple" to a tuple:

 julia> tuple(testtuple...,testvar)

(1,2,3,4)

julia> tuple = (1,2,3)

Warning: imported binding for tuple overwritten in module Main

(1,2,3)

julia> tuple(testtuple...,testvar)

ERROR: type: apply: expected Function, got (Int64,Int64,Int64)

For your second example, zip(tuplearray...) is actually about right.  The main differences from what you want are

1) it returns an iterator, not a set of arrays

2) the iterator yields tuples, not arrays

julia> zip(tuplearray)

Zip{(Array{(Int64,Int64,Int64),1},)}(([(1,2,3),(10,20,30),(100,200,300)],))

julia> collect(zip(tuplearray...))

3-element Array{(Int64,Int64,Int64),1}:

 (1,10,100)

 (2,20,200)

 (3,30,300)

Cheers,

   Kevin

[yaois...@gmail.com]

Ah, thank you!

This Google group community is fantastic.

[yaois...@gmail.com]

One more tuple question -- I am trying to find a tuple associated with a minimum x[n].

So taking let's say

tuplearray = [(3,2,1),(1,2,3),(3,1,2)]

I want to to find the min x[2] for x in tuplearray

minx2tuple = (3,1,2)

Using the method Kevin showed above, I can unpack the tuples to get three element arrays
 

x1array,x2array,x3array = collect(zip(tuplearray...))

Then, I can do

minx2 = minimum(x2array)

to get

minx2 = 1

However, if I do a comprehension,

[x for x in tuplearray if x[2] == minx2]

or

[x for x in tuplearray if x[2] == 1]

this comprehension does not work. The error I get is -- ERROR: syntax: unexpected "]".

How can I fix the comprehension to make it work in Julia?

Thanks,
Wally

[Leah Hanson]

Here's one way to go about it:

~~~

julia> tuplearray = [(3,2,1),(1,2,3),(3,1,2)]

3-element Array{(Int64,Int64,Int64),1}:

 (3,2,1)

 (1,2,3)

 (3,1,2)

julia> minimum(tuplearray)

(1,2,3)

julia> minimum(x->x[2],tuplearray)

1

julia> find(x->x[2]==1,tuplearray)

1-element Array{Int64,1}:

 3

julia> tuplearray[3]

(3,1,2)

~~~

Similarly, if you want to use your x2array:

~~~

julia> x2array = [2,2,1]

3-element Array{Int64,1}:

 2

 2

 1

julia> minimum(x2array)

1

julia> find(x->x==1,x2array)

1-element Array{Int64,1}:

 3

~~~

[yaois...@gmail.com]

Sweet, this is an incredibly fun language. Thanks!