How to search and find array in array?

Hello,

I create an array below;

bigArray = rand(1,150);
bigArray(1,15:19) = [1 1 1 1 1]';
bigArray(1,25:29) = [1 1 1 1 1]';
bigArray(1,75:79) = [1 1 1 1 1]';
bigArray(1,105:109) = [1 1 1 1 1]';
bigArray(1,65) = 1;
bigArray(1,5:6) = [1 1]';

I want to find [1 1 1 1 1]' array indexes. But I run the code;

idx = find(ismember(bigArray,[1 1 1 1 1]'))

idx = 1×23

5 6 15 16 17 18 19 25 26 27 28 29 65 75 76 77 78 79 105 106 107 108 109

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I want to see as an output; [15 16 17 18 19 25 26 27 28 29 75 76 77 78 79 105 106 107 108 109]

Answer 1

[Star Strider]

The ismember function is doing exactly what it should. You need to examine ‘bigArray’ tto understand its output.

Try this —

bigArray = rand(1,150);
bigArray(1,15:19) = [1 1 1 1 1]';
bigArray(1,25:29) = [1 1 1 1 1]';
bigArray(1,75:79) = [1 1 1 1 1]';
bigArray(1,105:109) = [1 1 1 1 1]';
bigArray(1,65) = 1;
bigArray(1,5:6) = [1 1]';

disp(bigArray)

  Columns 1 through 18

    0.5068    0.9505    0.0516    0.0882    1.0000    1.0000    0.0318    0.3127    0.8880    0.0266    0.9131    0.8241    0.3292    0.0973    1.0000    1.0000    1.0000    1.0000

  Columns 19 through 36

    1.0000    0.4800    0.7703    0.2106    0.1942    0.6979    1.0000    1.0000    1.0000    1.0000    1.0000    0.4912    0.4754    0.2845    0.7561    0.9840    0.1853    0.1938

  Columns 37 through 54

    0.4194    0.0772    0.1116    0.3382    0.2339    0.0543    0.3256    0.9436    0.2975    0.6174    0.2227    0.7096    0.5371    0.9033    0.7377    0.5522    0.5055    0.3581

  Columns 55 through 72

    0.8638    0.2271    0.3195    0.0197    0.4622    0.0299    0.3055    0.4705    0.3989    0.4399    1.0000    0.6735    0.8151    0.1478    0.8166    0.2860    0.6436    0.8295

  Columns 73 through 90

    0.4801    0.7913    1.0000    1.0000    1.0000    1.0000    1.0000    0.8977    0.8132    0.6884    0.4697    0.2341    0.1666    0.4997    0.6061    0.5467    0.4436    0.5024

  Columns 91 through 108

    0.8998    0.2705    0.0215    0.1483    0.4976    0.9649    0.5099    0.9422    0.8145    0.3519    0.6390    0.0093    0.5664    0.9736    1.0000    1.0000    1.0000    1.0000

  Columns 109 through 126

    1.0000    0.7624    0.4387    0.6305    0.1326    0.6353    0.2669    0.3236    0.1274    0.4486    0.2744    0.5949    0.0264    0.7638    0.9727    0.1876    0.1710    0.6894

  Columns 127 through 144

    0.3853    0.9315    0.9158    0.8965    0.2594    0.0620    0.3116    0.6300    0.4641    0.4008    0.7085    0.1320    0.1949    0.4087    0.7125    0.2770    0.0934    0.5674

  Columns 145 through 150

    0.4633    0.3660    0.7867    0.9442    0.3935    0.3620

Lv = ismember(bigArray,[1 1 1 1 1]')

Lv = 1x150 logical array
  Columns 1 through 45

   0   0   0   0   1   1   0   0   0   0   0   0   0   0   1   1   1   1   1   0   0   0   0   0   1   1   1   1   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

  Columns 46 through 90

   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   0   0   0   0   0   0   0   0   0   1   1   1   1   1   0   0   0   0   0   0   0   0   0   0   0

  Columns 91 through 135

   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   1   1   1   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

  Columns 136 through 150

   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

idx = find(Lv)

idx = 1×23

5 6 15 16 17 18 19 25 26 27 28 29 65 75 76 77 78 79 105 106 107 108 109

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.

[Hilal]

Thank you but I do not want to see 5 6 and 65 indexes. I just need 5 times repeated value indexes as an output. Also it should be faster than for loop.

[Star Strider]

To search for a specific pattern, use the strfind functiion. (It seems counterintuitive to use that here, however it works, after a fashion).

bigArray = rand(1,150);
bigArray(1,15:19) = [1 1 1 1 1]';
bigArray(1,25:29) = [1 1 1 1 1]';
bigArray(1,75:79) = [1 1 1 1 1]';
bigArray(1,105:109) = [1 1 1 1 1]';
bigArray(1,65) = 1;
bigArray(1,5:6) = [1 1]';

disp(bigArray)

  Columns 1 through 18

    0.2743    0.2407    0.8275    0.0096    1.0000    1.0000    0.8060    0.9308    0.5000    0.8108    0.5384    0.8746    0.4255    0.4682    1.0000    1.0000    1.0000    1.0000

  Columns 19 through 36

    1.0000    0.8638    0.2319    0.3997    0.2898    0.1223    1.0000    1.0000    1.0000    1.0000    1.0000    0.1297    0.7206    0.1497    0.6789    0.5847    0.5892    0.7993

  Columns 37 through 54

    0.2800    0.9085    0.7488    0.2514    0.1398    0.6313    0.5854    0.5353    0.4922    0.5730    0.1827    0.1280    0.9387    0.7217    0.2021    0.0497    0.3776    0.1897

  Columns 55 through 72

    0.2701    0.6038    0.7225    0.8177    0.6791    0.4523    0.2733    0.2405    0.7571    0.2166    1.0000    0.7963    0.6565    0.4824    0.2540    0.5467    0.0953    0.0753

  Columns 73 through 90

    0.4202    0.5929    1.0000    1.0000    1.0000    1.0000    1.0000    0.4567    0.3059    0.8577    0.0012    0.2719    0.9140    0.5484    0.2816    0.5734    0.8117    0.6676

  Columns 91 through 108

    0.5733    0.8570    0.0506    0.4219    0.2212    0.6640    0.7136    0.5508    0.5685    0.0510    0.7710    0.4171    0.2690    0.0529    1.0000    1.0000    1.0000    1.0000

  Columns 109 through 126

    1.0000    0.4731    0.3191    0.4956    0.4133    0.3051    0.1663    0.6878    0.8143    0.6790    0.9396    0.2974    0.8329    0.4112    0.1258    0.7320    0.4892    0.6529

  Columns 127 through 144

    0.9542    0.6012    0.7828    0.5601    0.3783    0.7228    0.5640    0.1776    0.6977    0.3227    0.6249    0.0279    0.2191    0.9455    0.1715    0.1862    0.7512    0.2973

  Columns 145 through 150

    0.7227    0.7914    0.1098    0.6703    0.2003    0.1265

pattern = [1 1 1 1 1];
Idx = strfind(bigArray,pattern);

Idx = 1×4

15 25 75 105

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Idx = reshape([Idx(:) Idx(:) + repmat((1:numel(pattern)-1), numel(Idx), 1)].', 1, []);

disp(Idx)

    15    16    17    18    19    25    26    27    28    29    75    76    77    78    79   105   106   107   108   109

The strfind function returns only the first index of the pattern, so it is necesary to add:

(1:numel(pattern)-1)

to each element. I did that here by transposing the original ‘Idx’ vector (the Idx(:) step), and summing it with that vector to create a matrix, then contatenating the transposed ‘Idx’ vector to the matrix I created in the first step, and then reshaped that to a row vector to get the desired result. It is not straightforward to get the result you want, however iit is definitely possiible.

The ismember function is quite useful at finding individual instances of the elements of its second argument, however it does not find patterns. There are other functions that operate similarly to strfind (the See Also section of the strfind function documentation page has a list of them), however strfind is a function everyone has.

.

[Hilal]

Thank you very much!

[Star Strider]

As always, my pleasure!