Combining variables

I have written a code that generates 20 strings (the number actually varies depending on the input), all of which have the names "s_idx_?" where ? is a number from 1 to 20. Is there a command that allows me to concatenate all these strings without having to type out all the names? Thanks.

[Nathan Greco]

First: it is generally nicer to create one data structure to contain all of these strings rather than creating a variable per string. Look up cell arrays, they are your friend. Rather than calling your strings s_idx_?, you could just call them s{?} where ? is your old number.

[E. Elgar]

Actually I'm oversimplifying the problem a bit. This is the code I have:

for e = 1:length(c)

f = eval(c{e}); % for each c, f gives the list of cues under the condition

for g = 1:length(f) % runs through the whole string of cues (f)

i = f{g};

h = genvarname('s_idx_',who);

eval([h '= find(strcmp(''' i ''',theData.study.cue))']); % matches each i with a number from some list I have

end

end

The output is a bunch of variables called "s_idx_?". The number of variables will change if I change the input. I've tried creating cell arrays as Nathan suggested, but it doesn't seem to work.

[Sean de Wolski]

POISON!! EVAL!! Don't do it!!

[E. Elgar]

!! Other solutions then?

[Stephen23]

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Sean de Wolski]

FAQ4.6

Don't do it!

but if you have to:

sprintf('s_idx_%i\n',1:20)

[Jan]

I agree with "Don't do it". The SPRINTF command concatenates the _names_ of the variables?! The OP wants to cat the string values.

Answer 2

[Jan]

Follow Sean's link to the FAQ. There you find the suggestion to use a cell like "s_idx{i}" instead of including the index in the name of the variables. Thjen the concatenation is easy:

s = cat(2, s_idx{:});

[E. Elgar]

Thank you! I think this will work.