How to delete a row if it doesn't follow a pattern
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Hi, I have... a = [ 2 5 1; 3 6 2; 3 4 1; 9 4 2; 8 3 1; 3 2 2; 9 5 2; 4 8 1]
Notice how the last column follows a pattern of 1, 2,1,2..and so on.
The 7th row however has a 2 in the last column just like the 6th row before...thus does not follow the pattern.
How would I delete the 7th row and any other row if it does not follow the 1,2,1,2 pattern of the last column?
Thanks.
2 commentaires
James Tursa
le 8 Juil 2015
Is the pattern always two different numbers alternating? Or could it be something else?
Réponse acceptée
Ashmil Mohammed
le 8 Juil 2015
Try out this code :
p=size(m,1);%m is your matrix
for i=1:p
if mod(i,2)==1 && m(i,size(m,2))~=mod(i,2)
m(i,:)=[];
p=p-1;
elseif mod(i,2)==0 && m(i,size(m,2))~=(mod(i,2)+2)
m(i,:)=[];
p=p-1;
end
end
Plus de réponses (2)
bio lim
le 8 Juil 2015
a = [ 2 5 1; 3 6 2; 3 4 1; 9 4 2; 8 3 1; 3 2 2; 9 5 2; 4 8 1];
% First lets remove 2's in a row
ii = 1:2:length(a);
b = a(ii,end)~=1;
a(2*find(b==1)-1, :) = [];
% Second lets remove 1's in a row
jj = 2:2:length(a);
c = a(jj,end)~=2;
a(2*find(c==1)-1,:) = [];
Output is
a =
2 5 1
3 6 2
3 4 1
9 4 2
8 3 1
3 2 2
4 8 1
0 commentaires
James Tursa
le 8 Juil 2015
Modifié(e) : James Tursa
le 8 Juil 2015
Assuming the pattern in the last column must be 1-2-1-2-...etc exactly
[m,n] = size(a);
expected = 1; % initialize expected value in 1st row
x = false(m,1); % initialize the deletion flag array
for k=1:m
if( a(k,n) ~= expected )
x(k) = true; % if not as expected, mark for deletion
else
expected = 3 - expected; % if as expected, update expected
end
end
a(x,:) = []; % delete the unexpected pattern rows
2 commentaires
James Tursa
le 8 Juil 2015
Modifié(e) : James Tursa
le 8 Juil 2015
Note: My answer and coffee's answer differ in how they treat a matrix that starts with a 2 in the last column of row 1 (and potentially the adjacent rows). My answer will delete all beginning rows until a 1 is found. coffee's answer does something different. If you want to allow beginning with a 1 or a 2, alter the expected initialization line as follows (assumes a(1,n) has to be either a 1 or a 2 and can't be anything else):
expected = a(1,n); % initialize expected value in 1st row
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