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Is there a lookup function in matlab?

Asked by John on 6 Jan 2013

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

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Answer by Image Analyst on 6 Jan 2013

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.
```

Walter Roberson on 7 Jan 2013
```convert = { 1 'AA'; 2 'AC'; 3 'DC'; ... }
```
```letterCodes = convert(states, 2);
```
John on 7 Jan 2013

Thank you, it works.

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

John

Walter Roberson on 7 Jan 2013

This is just array indexing of a cell array.

Answer by Walter Roberson on 7 Jan 2013

Also you could look at containers.map