How to make this simple script faster?
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Each of the Sta{i}.test is a one-column data with unknown number of rows. As you know, to keep expanding Variable X is not the most efficient way of doing this.
Is there a way I can get my X values faster without writing a loop?
X = [];
for i = a:b
if isfield(Sta{i}, 'test')
X = [X; Sta{i}.test];
end
end
Many thanks!
1 Commento
Image Analyst
il 3 Feb 2020
Modificato: Image Analyst
il 3 Feb 2020
Are you saying that sometimes the structure inside the cell might not have a field called "test"? What if you just allocated X as, say, 10 million elements or way more than you ever expect to have, then crop to the proper length after the loop. See my Answer below (scroll down).
Risposta accettata
Image Analyst
il 3 Feb 2020
Modificato: Image Analyst
il 3 Feb 2020
Does this work:
X = zeros(10000000, 1);
a = 1;
b = length(Sta);
lastIndex = 0
for i = a:b
if isfield(Sta{i}, 'test')
t = Sta{i}.test;
lt = length(t);
X(lastIndex+1:lastIndex+lt) = t;
lastIndex = lastIndex + lt;
end
end
X = X(1:lastIndex);
What is the size of Sta? How many elements does it have?
3 Commenti
Image Analyst
il 3 Feb 2020
Modificato: Image Analyst
il 3 Feb 2020
It might be. I experimented with doing things like (:) and {:} and putting stuff in brackets and using vertcat() but I just couldn't find the exact syntax that would do it. You'd have to experiment around some.
Can you store them in a more convenient way in the first place?
Più risposte (1)
David Hill
il 3 Feb 2020
You could preallocate X with nan to the largest expected and then delete the excess nan's at the end.
X = nan(10000000,1);
count=1;
for i = a:b
if isfield(Sta{i}, 'test')
temp=count+length(Sta{i}.test);
X(count:temp-1) = Sta{i}.test;
count=temp;
end
end
X=X(~isnan(X));
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