How to remove rows?

1 次查看（过去 30 天）
Justyna Slawska
Justyna Slawska 2016-12-15
回答： Steven Lord 2016-12-15
mydata = importdata('data.txt'); A=mydata;
nRows = size(A, 1);
nColumns = size(A,2);
for i=1: nRows
if (nnz(A(i,:)<3540) == 15)
A(i,:)=[];
end
end

请先登录，再回答此问题。

采纳的回答

José-Luis
José-Luis 2016-12-15
You don't need to loop
A(sum(A < 3540, 2) == 15,:) = [];

更多回答（1 个）

Steven Lord
Steven Lord 2016-12-15
If you must loop (a requirement of a homework assignment, for instance) inside the loop you should not actually delete the rows of the matrix. Instead record which rows need to be deleted and delete all of them after the loop is complete. Why?
x = 1:10;
n = numel(x);
for k = 1:n
fprintf('x contains %d elements, processing element %d of %d.\n', ...
numel(x), k, n);
if mod(x(k), 2) == 0
x(k) = [];
end
end
In this code you're shortening x every other iteration, and eventually you "walk off the end" of the array. Unlike Bugs Bunny, MATLAB notices immediately. Instead of chopping pieces off the array immediately, identify which pieces need to be removed then remove then once identification is complete.
x = 1:10;
n = numel(x);
toBeDeleted = false(size(x));
for k = 1:n
fprintf('x contains %d elements, processing element %d of %d.\n', ...
numel(x), k, n);
if mod(x(k), 2) == 0
toBeDeleted(k) = true;
end
end
x(toBeDeleted) = []

类别

在 Help Center 和 File Exchange 中查找有关 Logical 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by