Incremental indexing to create an array

Hi,

I have a 1097x1097 array (called list_of_distances) and would like to index into that array repeatedly; I only need certain values from the array. By doing this repeated indexing, I'd like to create new array that is 1x1097 of values. I included a screen shot of the values I'm looking to get into a new array.

Any help would be appreciated

Michael

Michael

R = 2
S = 1

for i = length(list_of_distances)
    final_list(i) = list_of_distances(R,S)
    R = R+1
    S = S+1
end
    

Answer 1

[Peng Li]

using diag(list_of_distances, -1) to get the diagonal you want.

[Peng Li]

and btw, this is off main diagonal so you won't be able to get a 1*1097 vector, 1096 instead.

[Michael King]

Thanks so much for the quick answer! looking forward to testing this out!

[Michael King]

It worked really well. A much more concise solution! Would you (or anyone) be able to take a minute to suggest what I was doing wrong with my for loop?

[Peng Li]

the loop doesn't run as your i is fixed at length(list_of_distances), and you prob want to do for i = 1:length(list_of_distances), but this way you are up to an indexing error as I commented above, you aren't able to have a vector of 1097 elements. Do for i = 1:size(list_of_distances, 1)-1 instead.

And you don't necessarily need to do a loop, although you are not familiar with some of these builtin functions. For this case, you can do list_of_distances(2:size(list_of_distances, 1)+1:end), which will give you the same results as diag(list_of_distances, -1).

list_of_distances = magic(10)

list_of_distances =

    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

>> b = diag(list_of_distances, -1)

b =

    98
    81
    19
     2
    90
    48
    31
    44
    27

>> c = list_of_distances(2:size(list_of_distances)+1:end)

c =

    98    81    19     2    90    48    31    44    27

[Michael King]

thanks, I've learned a lot here! much appreciated