how to access an array using a string?

I have 5 arrays which store the past 100 values related with 5 entities of a time series. time series contains of data values and each data value has one corresponding entity.

z = dataset('XLSFile','timeseries.xlsx');

    var1_a = z(9698:9797);
    var2_a = z(23298:23397);
    var3_a = z(93372:93471);
    var4_a = z(127688:127787);
    var5_a = z(206878:206977);

% each array is of 100 elements.
% for future values of time series, I need to call one of the array to add 
% 'new data value' to it and delete the oldest one out of it.
%I tried calling the array using 'strcat'.

    same_val = strcmp(next element,'var1_a');

% 'next element' is any one from var1, var2, var3, var4 or var5. 
% I need to access var1_a, var2_a.. and so on respectively for detected 'next element,.

        if (condition is satisfied)
            ary = strcat(next element,'_a');

            ary = [ary(2:100);new data value];

        else
        (do something else) 
        end

but I am getting error for this. What should be the right way?

Answer 1

[Star Strider]

I have no idea what you’re doing, but the way you are doing it is inefficient if not just wrong.

Use a cell array instead:

      var_a{1} = z(9698:9797);
      var_a{2} = z(23298:23397);
      var_a{3} = z(93372:93471);
      var_a{4} = z(127688:127787);
      var_a{5} = z(206878:206977);

You can then access them easily in a loop.

[na ja]

thanks strider, that helped!

[Star Strider]

My pleasure!

Answer 2

[Joe Yeh]

You can store data in a structure

    s = struct;
    s.var1 = z(9698:9797);
    s.var2 = z(23298:23397);
    s.var3 = z(93372:93471);
    s.var4 = z(127688:127787);
    s.var5 = z(206878:206977);

The field name of a structure is by itself a string.

You can either access the field by :

    s.var1

Or, if you store the string value in another variable, you can access the field by wrapping the variable in parentheses.

    tempvar = 'var1';
    s.(tempvar)  % this is equal to s.var1

[na ja]

Hi Joe, I have s structure field named d.NL330260 and a temporary variable grade_n which is a 1x1 cell array containing 'NL330260'. I tried implementing the following:

grade_n = 'NL330260';

d.(grade_n)

but , I get this error message.

Argument to dynamic structure reference must evaluate to a valid field name.

What could be the problem??

[na ja]

OK, solved it. I put it in this way:

   grade_n = 'NL330260';
    d.((char(grade_n) ))

Answer 3

[Walter Roberson]

Cell array and structures are good ways to handle this. You can also consider using table() objects and using container.map()

[na ja]

thanks walter