how to extract specific rows of a .txt file ?

I have a problem with a code. I have a file with several rows and columns. Some rows, especially the first six numbers of them, are repeated line by line.

I want a final output that includes only the rows of which the first 6 numbers are repeated.

for example I attach an example of the input and of the output of what I mean

could you please help me?

Answer 1

[Voss]

M = readmatrix('input.txt');
M(:,end) = [];
[~,~,jj] = unique(M,'rows','stable');
M([false; diff(jj) == 0],:) = [];
writematrix(M,'output.txt','delimiter','\t');

% check the output file:
type output.txt

1	2	3	5	6	8
2	4	6	8	9	6
3	5	6	8	9	10
2	4	6	8	9	6
7	8	9	10	22	6
8	7	9	6	2	5

[Ivan Mich]

ok, thank you. I have one more question. How could I count the number of the unique lines/rows? I have tried commands accumarray, but command window shows me

Error using accumarray

Too many output arguments.

for example i want to have an output like:

1 2 3 5 6 3

2 4 6 8 9 1

3 5 6 8 9 2

2 4 6 8 9 1

7 8 9 10 22 1

8 7 9 6 2 4

the last column includes the number of the repetitions of each line.

could you please help me?

[Voss]

M = readmatrix('input.txt');
M(:,end) = [];
[~,~,jj] = unique(M,'rows','stable');
M([false; diff(jj) == 0],:) = [];
M(:,end+1) = diff(find(diff([0; jj; 0])));
writematrix(M,'output.txt','delimiter','\t');

% check the input and output files:
type input.txt

1	2	3	5	6	8	5
1	2	3	5	6	8	4
1	2	3	5	6	8	3
2	4	6	8	9	6	5
3	5	6	8	9	10	3
3	5	6	8	9	10	9
2	4	6	8	9	6	2
7	8	9	10	22	6	3
8	7	9	6	2	5	1
8	7	9	6	2	5	4
8	7	9	6	2	5	8
8	7	9	6	2	5	6

type output.txt

1	2	3	5	6	8	3
2	4	6	8	9	6	1
3	5	6	8	9	10	2
2	4	6	8	9	6	1
7	8	9	10	22	6	1
8	7	9	6	2	5	4