Why does str2num take much longer to convert 1001 long char array apposed to a 1000 long char array (MatLab R2010b 64bit, on Win 64bit)
3 vues (au cours des 30 derniers jours)
%make 1001-by-3 char array of numbers, can replace 3 with any size
t = '0123456789';
t = t(ceil(rand(3,1001)*10))';
%big difference in time needed to convert 1000 vs 1001 numbers
tic,n1000 = str2num(t(1:1000,:));toc
tic,n1001 = str2num(t(1:1001,:));toc
% Elapsed time is 0.000285 seconds.
% Elapsed time is 0.011493 seconds.
%results are identical
all(n1000 == n1001(1:1000))
Walter Roberson le 1 Juin 2016
You should use timeit() from the File Exchange to get more accurate timing. (timeit was eventually made part of MATLAB.)
I do see more of a difference than I would expect in R2016a on OS-X.
I recommend you switch to str2double()
Steven Lord le 11 Mar 2023
What's your ultimate goal here, of which I suspect this conversion is one step in a larger process?
If you want to generate 1000 (or 1001) 3-digit numbers I wouldn't work with char arrays at all. Just create the data as numbers in the first place.
x = randi([100 999], 1001, 1);
If you're trying to convert data that you read in from a file as text into numbers, why not read that data in as numbers in the first place? If you're using functions like readtable or readmatrix set the import options created by detectImportOptions to read the data in using a numeric data type.
If you're trying to do something else and you can explain that task in more detail we may be able to offer more specific suggestions.