Hello,
Le 03/07/2015 09:42, jaipur a écrit :
I'm making a big structure (about 110,000 items) by reading data from
Hipparcos star catalog text file.
My procedure is as follows.
MyStruct = struct(); Index = 0;
while ~meof(Fd) do
........
........
Index = Index + 1;
MyStruct(Index).Field1 = ...;
MyStruct(Index).Field2 = ...;
MyStruct(Index).Field3 = ...;
end
But this procedure takes huge time!!
The number of items is known. Could you teach me speedy way to make big
structure?
For example, keep memory for structure before starting like
MyVector = ones(110000,1);
When creating new components of a structures array elements with an
*increasing* index, the time spent to create each one increases, and the
total time increases in a parabolic way:
-->clear s, tic; t=[]; for i=1:1000, s(i).n=%pi; if pmodulo(i,10)==0,
t(i/10)=toc(); end, end, toc()
ans =
52.603
-->plot(t)
Now, if components are created with a decreasing index, the time spent
to create each one is constant, and the total time varies in a linear way:
-->clear s, tic; t=[]; for i=1000:-1:1, s(i).n=%pi; if pmodulo(i,10)==0,
t(i/10)=toc(); end, end, toc()
ans =
5.553
-->plot(t)
Finally, initializing the array to its final size, and then filling its
components at increasing index is also fast and linear in time:
-->clear s, tic; t=[]; s(1000).n=0; for i=1:1000, s(i).n=%pi; if
pmodulo(i,10)==0, t(i/10)=toc(); end, end, toc()
ans =
5.696
Therefore, in your case, you may initialize:
MyStruct(110000).Field1 = 0;
MyStruct(110000).Field2 = 0;
MyStruct(110000).Field3 = 0;
and then assign the components as you did, at increasing index.
HTH
Samuel
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