Vectorising nested for loops
显示 更早的评论
Hi,
I’m trying to vectorise the following code snippet that works using the attached data. Unfortunately, I couldn’t succeed. Any ideas on how to deal with it?
Cheers,
Mel
k=0;
struct_data = struct('idx',[],'count',[],'size',[]);
for i = 1:size(table_data,1)
for j = 1:list(i)
k=k+1;
struct_data(k,1).idx = k;
struct_data(k,1).count = table_data.count(i);
struct_data(k,1).size = table_data.size(i);
end
end
2 个评论
Stephen23
2023-3-10
Are you intentionally storing lots of scalar cell arrays containing character vectors, or is the intent to actually just store the character vectors without the superfluous scalar cell arrays? If you only need the text, replace
table_data.size(i);
with
table_data.size{i};
Melanie VT
2023-3-10
采纳的回答
% unzip and load data
unzip data.zip
load data.mat
% run the loop method, for later comparison
k=0;
struct_data = struct('idx',[],'count',[],'size',[]);
for i = 1:size(table_data,1)
for j = 1:list(i)
k=k+1;
struct_data(k,1).idx = k;
struct_data(k,1).count = table_data.count(i);
struct_data(k,1).size = table_data.size{i}; % note this change:
% I made struct_data(k).size a char, instead of
% a scalar cell array containing a char
end
end
struct_data_save = struct_data;
% a "vectorized" method
idx = find(list);
struct_data = table2struct(removevars(table_data(repelem(idx,list(idx)),:),'district'));
C = num2cell(1:numel(struct_data));
[struct_data.idx] = deal(C{:});
% are the results the same?
isequal(struct_data,struct_data_save)
2 个评论
If you really want struct_data(k).size to be a 1x1 cell array containing a character vector (as in {'venti'}), as opposed to just a character vector (as in 'venti'), you can do it with a couple of additional lines of code:
% unzip and load data
unzip data.zip
load data.mat
% run the loop method, for later comparison
k=0;
struct_data = struct('idx',[],'count',[],'size',[]);
for i = 1:size(table_data,1)
for j = 1:list(i)
k=k+1;
struct_data(k,1).idx = k;
struct_data(k,1).count = table_data.count(i);
struct_data(k,1).size = table_data.size(i); % scalar cell array this time
end
end
struct_data_save = struct_data;
% a "vectorized" method
idx = find(list);
struct_data = table2struct(removevars(table_data(repelem(idx,list(idx)),:),'district'));
C = num2cell(1:numel(struct_data));
[struct_data.idx] = deal(C{:});
C = num2cell({struct_data.size});
[struct_data.size] = deal(C{:});
% are the results the same?
isequal(struct_data,struct_data_save)
Melanie VT
2023-3-10
更多回答（1 个）
S = load('data.mat')
list = S.list
tdat = S.table_data
k=0;
out0 = struct('idx',[],'count',[],'size',[]);
for i = 1:size(tdat,1)
for j = 1:list(i)
k=k+1;
out0(k,1).idx = k;
out0(k,1).count = tdat.count(i);
out0(k,1).size = tdat.size{i};
end % ^ ^ fixed indexing
end
out0
Without an explicit loop:
out1 = repelem(table2struct(removevars(tdat,'district')),list);
idx = num2cell(1:numel(out1));
[out1.idx] = idx{:}
isequal(out0,out1)
类别
在 帮助中心 和 File Exchange 中查找有关 Data Type Conversion 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
