Replace numeric values with symbols in an array

Question

The problem I'm facing is the following: I have been given an array of 6x1 which includes 2 NaN that represent 2 unknown values. What I want to do is replace these values with symbolic values (ie. x_1 and x_2 for example). What I don't understand what to do is if i'm given a 12x1 array for example with 10 NaN which I would have to change to X_1, X_2...X_10 in order to use the solver afterwards.

array = [0; 0; NaN; 0; 0; 0; 0; NaN; 0];

Change into:

array = [0; 0; x_1; 0; 0; 0; 0; x_2; 0];

But it has to be a general solution for arrays with different NaN's.

Thanks a lot in advance for your help and time.

You can't have a standard array containing numbers and symbolic variables. All entries must have the same data type. You could use a cell array to have each cell contain a different type. But that looks weird. Are you sure you need to mix numeric and symbolic contents? — Luis Mendo
– Luis Mendo, Commented Mar 15, 2017 at 22:43
Im given an array with NaN which represent variables, but since i'm programing a solver, the data provided can have 2, 3, 4 NaNs that are N variables. So in short I would like to find the first NaN an replace by x_1, the second by x_2... and then have an array with 0s and variables to run the solver on. Thanks for your time. — Asan
– Asan, Commented Mar 15, 2017 at 22:46
So you need a symbolic array? If that's the case, add the "symbolic-math" tag so someone with the knowledge can help — Luis Mendo
– Luis Mendo, Commented Mar 15, 2017 at 22:51
Yes, adding on what you said I could be given an array with NaNs and numerical values. But just the NaNs need to be changed into symbolic variables. So somehow I would need to have numerical values and symbolic systems in the array if possible, but There might be some other way around to the problem. — Asan
– Asan, Commented Mar 15, 2017 at 23:06

Teddy Ort · Accepted Answer · 2017-03-15 23:20:01Z

1

You can use the sym function:

array=sym(array);
array(isnan(array))=sym('x_',[sum(isnan(array)),1])

Explanation: The first line converts the array to a symbolic array. The second replaces the Nan elements with numerically indexed symbolic variables created by the sym function.

answered Mar 15, 2017 at 23:20

Teddy Ort

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Asan Over a year ago

This is exactly what I was looking for. Many thanks for your time.

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