Any simple way to change a struct with fields of length "n" to a struct of length"n"?
조회 수: 11 (최근 30일)
이전 댓글 표시
I have 2 structs each containing a field called 'time', along with other differently named fields of length "n"
i.e.
Mystruct.time = [1 4 6 8 9]
Mystruct.field2 = [5 6 7 8 9]
Mystruct.field3 = [23 423 2 4 7]
Yourstruct.time = [3 7]
Yourstruct.fieldX = [5 6]
What I need to do is create a time ordered "orderedStruct" that contains each index of these two structs, ordered by their time fields.
e.g. in this example I could type in "orderedStruct(num)" and could get the result:
orderedStruct(1) = struct with fields 'time' = 1, 'field2' = 5; 'field3' = 23;
orderedStruct(2) = struct with fields 'time' = 3, 'fieldX' = 5
orderedStruct(7) = struct with fields 'time' = 9, 'field2' = 9; 'field3' = 7;
Is there an efficient way to do this? I can imagine putting everything in a nested loop, from 1:number of structs and within that loop another going from 1:number of fields, but my structs could have 300 fields, with length of 50,000 or more. This would be a huge time hog.
Any ideas?
Thanks in advance
댓글 수: 5
Guillaume
2016년 3월 11일
Note that in an array of structure, all structures must have the same fields, so in your example orderedStruct must also have field2 and field3. What value should these be?
답변 (3개)
Jos (10584)
2016년 3월 11일
This question clearly shows how not thinking about your data management in the beginning will get you into trouble later on.
What do you want to have as the value of a field for which there is no time point ...?
댓글 수: 3
Guillaume
2016년 3월 11일
Regarding your latest comment, there is of course a simpler way to achieve the same thing, without eval and only looping once over the structures:
MyStruct = struct('Time', [1 4 6 8 9], 'field2', [5 6 7 8 9], 'field3', [23 423 2 4 7]);
YourStruct = struct('Time', [3 7], 'fieldX', [5 6]);
allstructs = {MyStruct, YourStruct}; %store structures in a cell array so we can iterate over them.
reshapedstructs = cell(size(allstructs));
timings = cell(size(allstructs));
%transform each struct from a struct of arrays into an array of structs of scalars
for sidx = 1:numel(allstructs)
fn = fieldnames(allstructs{sidx});
svalues = cell2mat(struct2cell(allstructs{sidx}));
reshapedstruct = cell2struct(num2cell(svalues), fn, 1); %the vertcat will fail if fields of the struct have different size
reshapedstructs{sidx} = num2cell(reshapedstruct'); %split the array of structs into a row cell array of scalar struct
timings{sidx} = allstructs{sidx}.Time;
end
%flatten the cell arrays and reorder by timing
reshapedstructs = [reshapedstructs{:}];
timings = [timings{:}];
[~, order] = sort(timings);
reshapedstructs = reshapedstructs(order);
celldisp(reshapedstructs)
A similar way to achieve the same in even less lines of code, but probably slower:
allstructs = {MyStruct, YourStruct};
reshapedstructs = cellfun(@(s) num2cell(cell2struct(num2cell(cell2mat(struct2cell(s))), ...
fieldnames(s), 1)'), allstructs, ...
'UniformOutput', false);
timings = cellfun(@(s) s.Time, allstructs, 'UniformOutput', false);
reshapedstructs = [reshapedstructs{:}];
timings = [timings{:}];
[~, order] = sort(timings);
reshapedstructs = reshapedstructs(order);
celldisp(reshapedstructs)
댓글 수: 0
Kelly Kearney
2016년 3월 11일
How about this?
A.time = [1 4 6 8 9];
A.field2 = [5 6 7 8 9];
A.field3 = [23 423 2 4 7];
B.time = [3 7];
B.fieldX = [5 6];
t = unique([A.time, B.time]);
[tf1,loc1] = ismember(A.time, t);
[tf2,loc2] = ismember(B.time, t);
flds = unique([fieldnames(A); fieldnames(B)]);
data = nan(length(flds), length(t));
for ii = 1:length(flds)
if isfield(A, flds{ii})
data(ii,loc1) = A.(flds{ii});
end
if isfield(B, flds{ii})
data(ii,loc2) = B.(flds{ii});
end
end
data = num2cell(data);
C = cell2struct(data, flds, 1);
You didn't specify how you wanted missing values or duplicated times to be treated. So in this example, times without a field value are indicated by NaNs, and any time that has data in both structures simply uses the data from the second one.
댓글 수: 2
Kelly Kearney
2016년 3월 12일
No, it would need to be modified a bit. Instead of preallocating data with NaNs, you'd need to set it up as a cell array, and add in a few num2cell's when assigning the numeric arrays to it. I'm away from my computer right now but I'll try to post a modified version later.
참고 항목
카테고리
Help Center 및 File Exchange에서 Structures에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!