Thread Subject: Assignment of a string to a variable

I have used a couple of different methods to achieve the
same goal of assigning a string to a variable. I am
interested to know if there is a better way and which way
that I have presented here is considered better.

Say I have a list of strings that can be configured by a
user to pluck out of the store what data the want:
params={'a';'b'};
I have stored in a file data corresponding to the variables
a, b, etc.
Store.a=[1 2 3];
Store.b=[4 5 6];
Alternatives are 1:
for ind=1:length(params)
    variable=char(strcat(params(ind),'avg'));
assignin('caller',variable,mean(eval(char(strcat('Store.',params(ind))))))
end

or 2:
for ind=1:length(params)
    variable=genvarname(strcat(params(ind),'avg'));
eval([variable
'=mean(eval(char(strcat(''Store.'',params(ind)))))'])
end

I cannot really see the benefit of genvarname here, and I am
not sure of advantages of assignin over eval if any. Is
there a better alternative?

Thanks
Andrew

"Andrew " <eatmyspam@mathworks.com> schrieb im Newsbeitrag
news:fm837f$edc$1@fred.mathworks.com...
>I have used a couple of different methods to achieve the
> same goal of assigning a string to a variable. I am
> interested to know if there is a better way and which way
> that I have presented here is considered better.
>
> Say I have a list of strings that can be configured by a
> user to pluck out of the store what data the want:
> params={'a';'b'};
> I have stored in a file data corresponding to the variables
> a, b, etc.
> Store.a=[1 2 3];
> Store.b=[4 5 6];
> Alternatives are 1:
> for ind=1:length(params)
> variable=char(strcat(params(ind),'avg'));
> assignin('caller',variable,mean(eval(char(strcat('Store.',params(ind))))))
> end
>
> or 2:
> for ind=1:length(params)
> variable=genvarname(strcat(params(ind),'avg'));
> eval([variable
> '=mean(eval(char(strcat(''Store.'',params(ind)))))'])
> end
>
> I cannot really see the benefit of genvarname here, and I am
> not sure of advantages of assignin over eval if any. Is
> there a better alternative?
>
> Thanks
> Andrew
>

Hi Andrew,
if it is O.K. I would definetely prefer to have the result again
as a cell array or structure:

params = {'a', 'b'};
meanValues = cell(size(params));
for i=1:length(params)
  res{i} = mean(Store.(params{i}));
end

or:
params = {'a', 'b'};
meanValues = [];
for i=1:length(params)
  meanValues.(params{i}) = mean(Store.(params{i}));
end

Both can be abbreviated by using structfun, but I wanted
to show how to use dynamic field names.

Titus

Using Dynamic Field Names, your code will be more simple

variable = strcat(p,'avg');

for ind=1:length(params)
   assignin('caller',variable{ind},mean(Store.(params{ind})));
end

Anh Huy Phan
RIKEN - BSI

"Anh Huy Phan" <phananhhuy@mathworks.com> wrote in message
<fm8572$o0m$1@fred.mathworks.com>...
> Using Dynamic Field Names, your code will be more simple
>
> variable = strcat(p,'avg');
>
> for ind=1:length(params)
> assignin('caller',variable{ind},mean(Store.(params{ind})));
> end
>
> Anh Huy Phan
> RIKEN - BSI
>
Thanks for the replies. The use of dynamic fields helps
because I also want to index selected elements in the data
to be assigned to the variable.

I have a further question and that is weather it is possible
to assign the variable to a structure within assignin such as
assignin('caller',Store.(variable{ind}),mean(Store ...

I know the input should be a string so I tried defining
variable with the structure name already so
variable{1} would be Store.a_avg, but again this did not
work. Failing this I can just store the variable in a
structure after the assignin command.

Thanks for all the help,
Andrew