How to label sorted variables

Hi,

Let say I have a matrix obtained from sort function,

x = [1,1,3;
     2,2,1;
     3,3,2]

with 1, 2, and 3 represent sorted values of certain variables in vertical manner alongside each column. I want to have another variable that stores the label of corresponding order.

% (e.g. It will be like this)
y = [A,A,B]

How can I do this if I have 7 variables that I want to sort in a 7-by-m matrix?

Thank you.

[dpb]

Save the optional second index array variable and use it to reference the label array.

Answer 1

[Matt J]

Maybe what you want:

>> labels=string({"A","B","C"});

>> x = [1,1,3;
     2,2,1;
     3,3,2];
 
>> labels(x)

ans = 

  3×3 string array

    "A"    "A"    "C"
    "B"    "B"    "A"
    "C"    "C"    "B"

[Arif Widianto]

Hi, Matt

Thank you for the answer. Actually it's not what I want. What I want is a label that represents a certain of order. (i.e. the order of [1,2,3] is labeled as A and [3,1,2] is labeled as B). So, if I have 3 variables there are 6 label possibilities and I can label it manually. However, actually I have a 7-by-m matrix with m is over than a 1000 which will be hard to label it manually.

[dpb]

factorial(7) ==> 5040.

What's your suggestion for labels?

[Arif Widianto]

Hi dpb,

Thank you for the response. Yes, exactly it is. I think 1-5040 would do.

[Stephen23]

Rather than creating a cell array of scalar string arrays and then converting that to a non-scalar string array:

string({"A","B","C"})

simply create the non-scalar string array right from the start:

["A","B","C"]

[dpb]

You'll have to save the perms(1:7) array and find the location of each column in it as the index/label, then.

A string match will probably be faster than all(ismember()) or the like.

[Matt J]

One thing you could do is create a label look-up table LUT, maintained a s a cell array

LUT=cell(1,2.^7);
vals=perms(1:7)*2.^(0:6).';
LUT(vals)=labels;

and now for a 7x3000 data set

[~,x]=sort(rand(7,3000)); %fake data

you would simply do

y=LUT(2.^(0:6) * x); %perform the label look-up