MATLAB: Traversing a long matrix

comparing rows of larger matrix

i've a matrix named A of size 2 x 16421

i want to compare one row with the other rows and whenever there is a match it spaecifies their index i mean which row number matches

A=[ 12 45
    32 56
    19 89
    12 45
     1  0
     0  0
    44 21
    32 56
    32 56
    12 45
    33 78
    90 32
    19 89 and so on....]

it starts with 12 45 and compare it with all other rows and shows there index value next it starts with 32 56 and compare it with other rows and when there is a match shows their index.

when i traverse it one by one it takes very long time can anybody tell me how can i do so?

Best Answer

I think this should work

ind = find(A(:,1) == A(:,2));

- Rob

Related Solutions

MATLAB: I need to know how to sum to the values of a specific column (identified by an index that can vary) of a generic matrix, a given column vector. For instance, how i decrease by 1 all the values of a column in a matrix (the rest remains the same)

Your question is rather confusing, as you seem to pose two different questions. I address both of these below:

>> A = magic(10)
A =
    92    99     1     8    15    67    74    51    58    40
    98    80     7    14    16    73    55    57    64    41
     4    81    88    20    22    54    56    63    70    47
    85    87    19    21     3    60    62    69    71    28
    86    93    25     2     9    61    68    75    52    34
    17    24    76    83    90    42    49    26    33    65
    23     5    82    89    91    48    30    32    39    66
    79     6    13    95    97    29    31    38    45    72
    10    12    94    96    78    35    37    44    46    53
    11    18   100    77    84    36    43    50    27    59
>> col = 6;
>> sum(A(:,col)) % the sum of one column
ans =  505
>> A(:,col) = A(:,col)-1 % decrease all values in one column
A =
    92    99     1     8    15    66    74    51    58    40
    98    80     7    14    16    72    55    57    64    41
     4    81    88    20    22    53    56    63    70    47
    85    87    19    21     3    59    62    69    71    28
    86    93    25     2     9    60    68    75    52    34
    17    24    76    83    90    41    49    26    33    65
    23     5    82    89    91    47    30    32    39    66
    79     6    13    95    97    28    31    38    45    72
    10    12    94    96    78    34    37    44    46    53
    11    18   100    77    84    35    43    50    27    59

MATLAB: I’ve a matrix of 6×4 and i want to count the rows how many times it occur in a matrix

A=[ 12 45 67 89
   34 56 78 65
   12 45 67 89
   53 55 21 90
   12 45 67 89
   53 55 21 90 ]
[a,b,c]=unique(A,'rows','stable');
v=arrayfun(@(x) sum(c==x),1:size(a,1))';
out=[a v]

Best Answer

Related Solutions

MATLAB: I need to know how to sum to the values ​​of a specific column (identified by an index that can vary) of a generic matrix, a given column vector. For instance, how i decrease by 1 all the values ​​of a column in a matrix (the rest remains the same)

MATLAB: I’ve a matrix of 6×4 and i want to count the rows how many times it occur in a matrix

Related Question

MATLAB: I need to know how to sum to the values of a specific column (identified by an index that can vary) of a generic matrix, a given column vector. For instance, how i decrease by 1 all the values of a column in a matrix (the rest remains the same)