extracting rows from large table
8 次查看(过去 30 天)
显示 更早的评论
I have a large table (23000000x11) and want to extract rows from the table based on values in the 5th column.
for example the data looks like:
66172 8:17 1 2 1 1 1 1 1 6 8
66842 7:17 1 3 0 1 1 1 1 1 7
.
.
.
and I want to create a smaller table with all the rows whose value of the fifth column are 0. This is of course easy to do with for loops and if statements, but takes enormous amounts of time to run. Is there a way using maybe ismember, intersect, or some other means to carry this out. I'm sure there must be. Any suggestions are appreciated.
0 个评论
采纳的回答
Walter Roberson
2022-9-30
mask = YourTable{:, 5} == 0;
subset0 = YourTable(mask, :);
3 个评论
Siddharth Bhutiya
2022-10-10
For the first line of code dot would be much faster than brace.
mask = YourTable.varName == 0; % if you know the name of your fifth variable
mask = YourTable.(5) == 0; % if you dont know the name.
Walter Roberson
2022-10-11
I was curious about the timing.
In my tests, the first 5 or so {:,5} accesses were reliably much slower than the others, so I skip those in the plot.
I must admit that I do not understand why {:,5} would be 5 or 6 times slower than .(5)
format long g
YourTable = array2table(randi(9, 5000, 7), 'VariableNames', {'a', 'b', 'c', 'd', 'e', 'f', 'g'});
N = 50;
skip = 7;
time_brace = zeros(N,1);
time_named = zeros(N,1);
time_dotnum = zeros(N,1);
for K = 1 : N
tic; YourTable.(5); t=toc(); time_dotnum(K) = t;
tic; YourTable{:,5}; t=toc(); time_brace(K) = t;
tic; YourTable.e; t=toc(); time_named(K) = t;
end
subset = [time_brace(skip+1:end), time_named(skip+1:end), time_dotnum(skip+1:end)];
plot(subset);
legend({'\{:,5\}', '.e', '.(5)'})
mean(subset)
更多回答(0 个)
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!