Allocating matrix / structure data instead of string name to variable

Question

I have a script that opens a folder and does some processing on the data present. Say, there's a file "XYZ.tif".

Inside this tif file, there are two groups of datasets, which show up in the workspace as

data.ch1eXYZ

and

data.ch3eXYZ

If I want to continue with the 2nd set, I can use A=data.ch3eXYZ

However, XYZ usually is much longer and varies per file, whereas data.ch3e is consistent.

Therefore I tried A=strcat('data.ch3e','origfilename'); where origfilename of course is XYZ, which has (automatically) been extracted before.

However, that gives me a string A (since I practically typed

A='data.ch3eXYZ'

instead of the matrix that data.ch3eXYZ actually is. I think it's just a problem with ()'s, []'s, or {}'s but Ican't seem to figure it out.

Thanks in advance!

It seems hard to avoid eval in this case. Try eval(['A = ' strcat('data.ch3e','origfilename') ';']) — Luis Mendo
– Luis Mendo, Commented Jun 27, 2014 at 14:18
Ah, the infamous eval. It works perfectly btw! Thanks for including the ';' too, probably would not have figured out where exactly to put it in. Eval keeps confusing me, maybe I'll remember this time. — user3783502
– user3783502, Commented Jun 27, 2014 at 14:25
As a general rule, if you need eval you probably should be doing things differently so that you don't need it. In this case, maybe use cells instead of fields. Oh, I see now that @excaza's answer solves it with dynamic field names. Clever — Luis Mendo
– Luis Mendo, Commented Jun 27, 2014 at 14:33

sco1 · Accepted Answer · 2014-06-27 14:36:48Z

3

If you know the string, dynamic field references should help you here and are far better than eval

Slightly modified example from the linked blog post:

fldnm = 'fred';
s.fred = 18;
y = s.(fldnm)

Returns:

y =

    18

So for your case:

test = data.(['ch3e' origfilename]);

Should be sufficient

Edit: Link to the documentation

edited Jun 27, 2014 at 14:36

answered Jun 27, 2014 at 14:24

sco1

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2 Comments

user3783502 Over a year ago

See, I didn't need a solution to my problem, just the correct way of what I wanted to do. Thanks a lot, works like a charm! :)

sco1 Over a year ago

@user3783502 It really should be better documented, I used MATLAB for more than 6 years before I discovered the syntax. It's extremely powerful on its own, even more so when compared to eval, which is generally used in its place.

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