Randi with string variables

Goodmorning everybody,

I'm trying to use the 'randi' function on Matlab (but this is for a script on Psychtoolbox). I would like to present a string value, instead of a numerical value. This is what I obtain :

First trial :

>> items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'};
>> randi(items{i});
*?? Subscript indices must either be real positive integers or logicals.>>*

Second trial :

>> items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'};
>> randi(items);
*??? Error using ==> randi
Inputs must be numeric.*

Third trial :

>> items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'};
>> randi(7)

ans =

       4

How Matlab can show me the string values specified in 'items' with randi?

Thanks!!

-Emilie

Answer 1

[Azzi Abdelmalek]

 items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'}
 n=numel(items);
  out=items(randi(n,n,1))

If you want to avoid repetition use

n=numel(items);
items(randperm(n))

[Emilie04]

Thank you :) That functions.

But I want to go father. I want that Matlab choses 1 value in the list, randomly and after its choice, it continues to read the list in the order defined in items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'};

For example : it choses, randomly 'saumon', and then it presents 'vélo' 'table', 'cochon'

Two problems : with this method, it always choses more than one items (and if I write randperm(1:7), that doesn't function).

>> items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'}; >> n=numel(items); >> SP=items(randperm(3))

StartPosition =

    'souris'    'voiture'    'lapin'

>> PositionOrder=[StartPosition:7 1:(StartPosition-1)] ??? Undefined function or method 'colon' for input arguments of type 'cell'.

Thanks !

[Jan]

@Emilie: The error message means, that "StartPosition" is a cell. It seems like you have confused the StartPosition, which is most likely an index, with the index contents.

Do not use randperm(1:7) but randperm(7).

Answer 2

[Jan]

I suggest to read the Getting Started chapters of Matlab. The documentation of randi (see "help randi", "doc randi") explain, that a number is replied and which inputs are needed. Then it is obvious that "randi(items)" must fail und you do not have to ask the forum for this.

items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'};
n = numel(items);
index = randi(n, 1);
selectedItems = items(index:n)

You see: "items" are your data, while "randi" and "index" are indicies only. To get the wanted indices, the actual data do not matter at all, therefore the creation of "index" does not require the contents of "item", but only its size.

Answer 3

[Daniel Shub]

Is this what you want?

items = {'lapin', 'souris', 'voiture', 'saumon', 'vÈlo', 'table', 'cochon'};
items(randi(length(items)):end)

[Emilie04]

Oh Yes thank you!!!! Two days on this function.

Tanks a lot :):)