Vectorizing multiple string comparison
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Paolo Binetti
el 26 de En. de 2017
Comentada: Paolo Binetti
el 28 de En. de 2017
Is there a way to significantly speed up this loop, perhaps by vectorizing it? Inputs in attachment. I do not have a Matlab version with "string" functions.
d = a';
for i = 1:numel(a)
d{i} = c(strcmp(a{i}, b), :);
end
I tried working my way from the inner part with cellfun, but either I am not getting it right or it is not the good approach:
aux = cellfun(@strcmp, a, b); % does not work
2 comentarios
Walter Roberson
el 27 de En. de 2017
That file is an Octave file that would take a bunch of work to read in MATLAB.
This is the wrong resource to be asking about performance improvement for Octave.
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Guillaume
el 26 de En. de 2017
One obvious minor speed-up is to get rid of the find that serves absolutely no purpose. You can directly use the logical vector returned by strcmp:
d{i} = c(strcmp(a{i}, b)), :);
For some reason, I cannot load your mat file. I'm going to assume that a is a cell array of string, and so is b (otherwise the loop would not be needed). Assuming that there are no repeated strings in b:
assert(numel(unique(b)) == numel(b), 'This code does not work when there are duplicate values in b');
d = cell(size(a))';
[isfound, loc] = ismember(a, b);
d(isfound) = c(loc(isfound), :);
If it's guaranteed that all elements of a are found in b, then you can simplify even further to:
assert(numel(unique(b)) == numel(b), 'This code does not work when there are duplicate values in b');
[isfound, loc] = ismember(a, b);
assert(all(isfound), 'The next line only works if all elements of a are in b');
d = num2cell(c(loc, :), 2);
2 comentarios
Guillaume
el 27 de En. de 2017
Editada: Guillaume
el 27 de En. de 2017
According to Walter, your mat file is an octave file that matlab can't open.
If there are duplicate values in b, then you don't have a choice but to use a loop, either explicitly as you have done or with cellfun:
d = cellfun(@(aa) c(strcmp(aa, b), :), a, 'UniformOutput', false);
It's very possible that the cellfun may be slower than the explicit loop (due to the anonymous function call).
edit: in matlab R2016b there is a an extremely easy way to vectorise the string comparison, using the new string class:
string(a) == string(b)'
but you'd still need a loop or cellfun afterward to create the d cell array:
d = cellfun(@(r) c(r, :), num2cell(string(a) == string(b)', 1), 'UniformOutput', false)
Más respuestas (1)
Walter Roberson
el 27 de En. de 2017
ismember can be used between cell arrays of strings. The two-output version can be used to find the indices, which you can then use to index into c.
3 comentarios
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