Is there a lookup function in matlab?

Hello,

I am simulating a markov chain using the code below.

      transC = [zeros(size(T,1),1), cumsum(T,2)]; %cumulative sum of rows, we will use this to decide on the next step.
    n = 10000;
    states = zeros(1,n); %storage of states
    states(1) = 32; %start at state 1 (or whatever)
    for ii = 2:n
       %Generate a random number and figure out where it falls in the cumulative sum of that state's trasition matrix row
       [~,states(ii)] = histc(rand,transC(states(ii-1),:));
    end

It combines a transition probability matrix and a random number to return a sequence of states. e.g 1,2,4,2,5,4,3.....

However, the states are actually letter codes, e.g AA, AC, DC

I have a have a variable called 'convert' where I have a list of the states and their corresponding letter codes. For example

1 AA
2 AC
3 DC
. . 
. .

How could I lookup the actual state names and return them in a new variable?

Thank you

Answer 1

[Image Analyst]

Presumably your variable is a cell array where the first column is the state number (kind of unnecessary actually) and the second column is the letter code. So to get the letter code from some variable stateNumber that contains an integer, you'd simply do:

letterCode = convert{stateNumber, 2}; % convert is your cell array variable.

[John]

Hello Image Analyst,

Thanks for your reply.

I'm sorry, I don't quite follow, do you mean I do the following?

transC = [zeros(size(T,1),1), cumsum(T,2)]; %cumulative sum of rows, we will use this to decide on the next step.
    n = 10000;
    states = zeros(1,n); %storage of states
    states(1) = 32; %start at state 1 (or whatever)
    for ii = 2:n
       %Generate a random number and figure out where it falls in the cumulative sum of that state's trasition matrix row
       [~,states(ii)] = histc(rand,transC(states(ii-1),:));
    end
letterCode = convert{state, 2}; % convert is your cell array variable.

Thank you

[Walter Roberson]

convert = { 1 'AA'; 2 'AC'; 3 'DC'; ... }

letterCodes = convert(states, 2);

[John]

Thank you, it works.

Is there documentation for this? I don't understand how it works, as silly as that sounds.

John

[Walter Roberson]

This is just array indexing of a cell array.

Answer 2

[Walter Roberson]

Also you could look at containers.map