Divide table takes a lot of calculation time

In my script i want to devide a table, it works for now, but it takes a lot of time.

How can i do this easier or faster?

reactionforce{3:end,:} = reactionforce{3:end,:}/1e10

Answer 1

[Guillaume]

I doubt you're using any feature of a table with a table that large so why not store your data in a matrix instead. Matrix operations will be slightly faster. Saying that, with your example table, the division takes 76 milliseconds on my computer. I would hardly call that a lot of time.

reactionforce = table2array(reactionforce);  %convert table to matrix since you don't use the features of tables
%...
reactionforce(3:end, :) = reactionforce(3:end, :) / 1e10;

[madhan ravi]

+1

[Jesse]

Thanks, on my computer it took about 20 seconds, so maybe that could also be the problem ;)

With this method it is much faster, about 1 second.

Thanks!

[Guillaume]

The contents of a table is always held as a cell array, with one table variable (column) per cell. Therefore, when you write reactionforce{3:end, :} = reactionforce{3;end, :}/1e10, matlab has to:

• concatenate all these cells into one big matrix. This involves copying the content of each variable into a new memory location
• extract the rows of the matrix that you asked for
• perform the division
• convert the result back into a cell array of column

So this is always going to take more time than just performing a division on a matrix. It's surprising that it's so slow on your machine though.