Vertical concatenation of structure fields

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Initial Conditions 2014-9-23

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https://ww2.mathworks.cn/matlabcentral/answers/155920-vertical-concatenation-of-structure-fields

评论： Kelly Kearney 2014-9-23

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.

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Answer 1

Kelly Kearney 2014-9-23

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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

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Initial Conditions 2014-9-23

Ok, simple mistake. The loop needs to be 1:length(fld2) not length(fld1)

Thanks!

Kelly Kearney 2014-9-23

Oops, yeah, typo.

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Answer 2

Guillaume 2014-9-23

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https://ww2.mathworks.cn/matlabcentral/answers/155920-vertical-concatenation-of-structure-fields#answer_152665

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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{:});

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Initial Conditions 2014-9-23

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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