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

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Julia
Julia 2023-2-13
评论： Julia 2023-2-13
Hi! If I have a matrix:
M= [1 50 60 70 50 40
2 NaN 10 20 10 10
3 NaN 20 NaN NaN NaN
1 NaN 60 30 40 50
2 10 20 10 20 NaN
1 30 20 40 NaN 50
2 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
KSSV
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
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.

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采纳的回答

Voss
Voss 2023-2-13
diff(find([M(:,1); 1] == 1))

更多回答（1 个）

Bhavana Ravirala
Bhavana Ravirala 2023-2-13
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
Hope this helps!!

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