如何基于同时应用于不同列的条件提取矩阵的行?

For example, say I have a 3-column matrix of news notifications, where the first column gives the serial number of news read in a sequence, the second column givess the Category of the news, and the third column gives whether the notification was opened or not (binary, 1 for read or 0 for not read). So, an excerpt might look like this:

例如,新闻通知,说我有一个三栏矩阵的第一列给新闻读一个序列的编号,第二列给新闻的类别,和第三列给是否通知被打开(二进制、1或0没有读过)。所以，一段摘录可能是这样的:

1    12     1
2    13     0
3    13     1
4    12     0
5    14     1
6    13     0
7    12     0
8    13     1
9    14     0
10   12     1

And I want all the rows where notifications from category 12 were read. So, the output should be this:

我要读取第12类通知的所有行。因此，输出应该是:

1    12     1
10   12     1

So, if the data matrix is called input, and the resultant matrix I want is named output, I would write the following code:

因此，如果数据矩阵被称为输入，而我想要的结果矩阵被称为输出，我将编写以下代码:

for i=1:size(input,1)
    temp = input(input(:,2)==12,:);
    output = temp(temp(:,3)==1,:);
end

But I suppose this should a trivial thing to do in MATLAB. So, is there a one liner that does this?

但我想这在MATLAB中应该很简单。有这样的内线吗?

2 个解决方案

#1

output=input(find(input(:,2)==12 & input(:,3)==1),:)

#2

Here is a solution using the supposed to be fast in-built function ismember, which is actually the dedicated function for what you want to achieve:

这里有一个解决方案，使用所谓的快速内置函数ismember，它实际上是你想要实现的目标的专用函数:

%// data
A =[1    12     1
    2    13     0
    3    13     1
    4    12     0
    5    14     1
    6    13     0
    7    12     0
    8    13     1
    9    14     0
    10   12     1]

%// sequence to search for
x = [ 12 1 ]

%// filtering
out = A( ismember(A(:,2:3),x,'rows'), : )

---

out =

     1    12     1
    10    12     1