Assign Multiple Variables

I have a array for example [1,2,3,4]. I want to assign a variable to each number in the array such that a=1, b=2, c=3, and d=4. I know I can do each one separately but I want to know if it is possible to this in one line.

[Image Analyst]

Kind of reminded me of the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F though I'm not saying you don't have a valid reason for doing that - you may well have.

Answer 1

[Walter Roberson]

It is not possible in one statement. It is possible in two statements, which you could combine on one line.

t = num2cell([1,2,3,4]);
[a,b,c,d] = deal(t{:});

[Fangjun Jiang]

Or could work without deal. [a,b,c,d] = t{:}

[Walter Roberson]

I don't believe I've see that documented. Based upon the descriptions of what {:} does, it would be reasonable to interpret it as equivalent to

[a,b,c,d] = t{1}, t{2}, t{3}, t{4}

which would be an invalid assignment (not enough output arguments) followed by three implicit disp()

[Fangjun Jiang]

It is documented. See Example 3 at the bottom of this page.

http://www.mathworks.com/help/techdoc/ref/deal.html

[Teja Muppirala]

You COULD do it in one statement, but, you probably wouldn't want to...

X = [10 20 30 40];
[a,b,c,d] = subsref(num2cell(X),struct('type',{'{}'},'subs',{{1:4}}))

[Edwin Fonkwe]

Hi Teja, I'm sorry if I sound rude, but this is a terrible implementation on Matlab!

[Daniel Bridges]

Edwin, have you seen Mathematica? From the introductory documentation I've read, it seems Wolfram wants users to code like that from the beginning ...

[Fangjun Jiang]

t = num2cell([1,2,3,4]);
[a,b,c,d] = deal(t{:})

a = 1

b = 2

c = 3

d = 4

[a,b,c,d] = t{:}

a = 1

b = 2

c = 3

d = 4

[Walter Roberson]

Back in 2011 it was not possible in one statement, at least not without an inline subsref(). A few years ago, however, a hack became available:

[a,b,c,d] = struct('x', num2cell([1,2,3,4])).x

a = 1

b = 2

c = 3

d = 4

Answer 2

[Raziman Thottungal Valapu]

It is now possible to do this in one line cleanly

[a,b,c] = deal(1, "test", [1:5])

Gives me

a =
     1
b =
    "test"
c =
     1     2     3     4     5

As expected

[Stephen23]

@Raziman Thottungal Valapu: no, that is not what the question is about. The question specifies that there is only one input array, but your code uses multiple separate inputs to deal. Not the same thing at all.

Answer 3

[Viktor]

The one-liner I have been using is the following:

[a,b,c,d] = feval(@(x) x{:}, num2cell([1,2,3,4]));

(Don't claim it is my original idea, just felt it belongs to this thread. If it is posted elsewhere feel free to link it.)

[Daniel Birch]

Additionally, you can replace num2cell with any cell array of the right size, even one containing multiple data types. For example,

[a,b,c,d] = feval(@(x) x{:}, {rand(2), 5, 'hello', pi});
a

a =

      0.9502    0.4387
      0.0344    0.3816

b

b =

       5

c

c =

hello

d

d =

      3.1416

[Stephen23]

That is just subsref wrapped up in an anonymous function, which is then called by feval.

Here it is with subsref called directly:

>> [a,b,c,d] = subsref({rand(2), 5, 'hello', pi}, substruct('{}',{':'}))
a =
 0.103676   0.814128
 0.208758   0.092132
b =  5
c = hello
d =  3.1416

Answer 4

[Jeff Miller]

matsplit does this.

[Stephen23]

+1 neat

[Brent F]

Much cleaner than deal(a(1), a(2), a(3), a(4), ...)

Answer 5

[Dan Erwin]

The thing we are trying to do is emulate the very useful Python idiom e.g.

a,b,c,d = [1,2,3,4]

In Matlab, if you create a function assignList.m as follows:

function varargout = assignList( inputArray )
for i = 1:length( inputArray)
    varargout{i} = inputArray(i);
end
end

then you can do for example

[a,b,c,d] = assignList( [1,2,3,4] )

[Fangjun Jiang]

deal or no deal in MATLAB can do this already.

[Stephen23]

@Fangjun Jiang: how? Please show how DEAL can be used with one vector/array input as shown.

[Fangjun Jiang]

@Stephen23, not with array input directly. See my comments at the answer by @Walter Roberson. My point is that this funciton is uncessary. Plus, I can't resist the "Deal or No deal" pun, now that I realized it.

[Dan Erwin]

I would not have written my post if I had noticed the earlier answer which recommended the contributed function matsplit, which is similar to mine but is more flexible when using multidimensional arrays.