How may I calculate the number of rows in each group?

Question

Julia 2023-2-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1911380-how-may-i-calculate-the-number-of-rows-in-each-group

评论： Julia 2023-2-13

Hi! If I have a matrix:

M= [1 50 60 70 50 40
NaN 10 20 10 10
NaN 20 NaN NaN NaN
NaN 60 30 40 50
10 20 10 20 NaN
30 20 40 NaN 50
NaN 50 50 NaN NaN]

The first column indicates to which group the rows belong to. "1, 2, 3" (row 1, 2, 3) are Group 1, "1, 2" (row 4, 5 ) are Group 2, the next "1, 2" ( row 6, 7) are Group 3.

I am trying to find the number of rows in each group. The desired result would be:

N= [3
    2
    2]

Could someone please teach me how to do this? It seems that I can't get my head around it. I think the first step can be splitting the groups:

g=nan(size(M,1),1);
ix=(M(:,1)==1);
g(ix)=[1:sum(ix)];
g=fillmissing(g,'previous');

but I am not sure where to go from here.

2 个评论
显示无隐藏无

KSSV 2023-2-13

Whats the logic for this?

"1, 2, 3" (row 1, 2, 3) are Group 1, "1, 2" (row 4, 5 ) are Group 2, the next "1, 2" ( row 6, 7) are Group 3

Dyuman Joshi 2023-2-13

编辑：Dyuman Joshi 2023-2-13

So when the value in first column is 1, a new group starts? If so, @Voss's answer should be good to go.

If not, then specify a general criteria for splitting into groups.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Voss 2023-2-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1911380-how-may-i-calculate-the-number-of-rows-in-each-group#answer_1170040

在 MATLAB Online 中打开

diff(find([M(:,1); 1] == 1))

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Julia 2023-2-13

Thank you! Your answer helps a lot.

请先登录，再进行评论。

Answer 2

Bhavana Ravirala 2023-2-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1911380-how-may-i-calculate-the-number-of-rows-in-each-group#answer_1170055

在 MATLAB Online 中打开

Hi Julia,

According to my understanding, the first element of the row is deciding the group. You can use the below code to know the number of rows in each group.

N=M(:,1);   % getting the first column of elements which we are using to divide the groups
k=length(N); % gives the number of rows in the matrix
j=[];
o=0;
for i=1:k
if(n(i)==1)
     if(o~=0)
        j=[j,o];
    end
o=1;
else   
o=o+1;
if i==k
        j=[j,o];
    end
end
end