Vertical concatenation of structure fields

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Hi,
I have a structure 'all' which has 45 fields with names 'day_X' where X goes from 1 to 45. Each 'day_X' level has 19 fields and it is these fields I want to concatenate. The fields are all vectors, and each Day_X struct has the same structure (fieldnames).
In other words, I want to vertically concatenate all.day_1.field1 through all.day_45.field1 , for each field. Is there an efficient way of doing this i.e., without a loop? I've tried numerous things, including a loop, but I know this can probably be done in a few lines.
Thanks in advance.

Accepted Answer

Kelly Kearney
Kelly Kearney on 23 Sep 2014
I'd do it with one loop and one cellfun. You might be able to eliminate the loop entirely, but this keeps it a little more readable, in my opinion.
all.day1.one = 1;
all.day2.one = 2;
all.day1.two = 3;
all.day2.two = 4;
fld1 = fieldnames(all);
fld2 = fieldnames(all.day1);
for ii = 1:length(fld1)
tmp = cellfun(@(x) all.(x).(fld2{ii}), fld1, 'uni', 0);
A.(fld2{ii}) = cat(1, tmp{:});
end
  3 Comments
Initial Conditions
Initial Conditions on 23 Sep 2014
Ok, simple mistake. The loop needs to be 1:length(fld2) not length(fld1)
Thanks!

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More Answers (1)

Guillaume
Guillaume on 23 Sep 2014
First of all, do not name your structure all as that shadows the name of a very useful matlab function.
Secondly, having a structure the way you've done it a bad idea (as you've just found out). You should have made the day field a structure array and the same with the field field.
Anyway, to answer your question:
c = cellfun(@(fn) all.(fn).field1, fieldnames(all), 'UniformOutput', false);
vertfield1 = vertcat(c{:});
  1 Comment
Initial Conditions
Initial Conditions on 23 Sep 2014
Thanks for the neat solution. I realised all was a bad name when I tried to 'clear all' and not every variable was cleared! Your solution works but I still have to cycle through all the 19 variables starting with 'field1' - but this could be done in a quick loop I think.

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