i m trying interpret this simple matrix code..

seed:345

10x7 matrix,

[-150,300]

B=randi...

and i want to sort 10 elements of row3 by ascending order.

i m wondering >>> %parts!

>> rand('seed',345)
>> B=randi([-150,300],10,7)
B =

  -148    86   -67    36   -15  -141   195
   -38   177    41   124   266    74   284
    27    95    32   107    45   204   206
    76   182    11   269   -78   -80  -100
   -34   275  -138   238   -48    20    15
   171  -119    88   108   -79   195  -118
    19   134    12    76   -35  -131   138
   285   228   -78   148    -9  -107   -55
   225    23   147    20   -73   155   237
   -18   247   279    17   277   222    71

>> [y,in]=sort(B(:,3)) %using [y,in] this two variables because this is matrix with line,row
                       %so i m usinng two variables right?
                       %and i can change 'y','in' to another chracters right?
                       
y =

  -138
   -78
   -67
    11
    12
    32
    41
    88
   147
   279

in =

    5
    8
    1
    4
    7
    3
    2
    6
    9
   10

>> B(in(1:end),:)  

   
   ans =

   -34   275  -138   238   -48    20    15
   285   228   -78   148    -9  -107   -55
  -148    86   -67    36   -15  -141   195
    76   182    11   269   -78   -80  -100
    19   134    12    76   -35  -131   138
    27    95    32   107    45   204   206
   -38   177    41   124   266    74   284
   171  -119    88   108   -79   195  -118
   225    23   147    20   -73   155   237
   -18   247   279    17   277   222    71

Answer 1

[Voss]

rand('seed',345)
B=randi([-150,300],10,7)

B = 10×7

280 -19 68 -82 48 124 -130 240 129 -112 166 15 295 -20 249 300 200 -65 232 266 298 206 144 170 236 -78 150 -26 128 -19 166 86 235 48 -51 159 298 78 117 300 66 -2 -146 247 221 34 50 -102 -143 273 18 41 109 30 222 73 26 -65 -70 -149 89 49 242 121 139 -40 -97 286 120 161

[sorted_B_column_3,old_indices_in_B_column_3]=sort(B(:,3))

sorted_B_column_3 = 10×1

-112 -70 -40 41 68 78 166 170 200 221

old_indices_in_B_column_3 = 10×1

2 9 10 8 1 6 5 4 3 7

%using [y,in] this two variables because this is matrix with line,row
%so i m usinng two variables right?

% it's two variables because that's two outputs from the sort() function:
% (1) the sorted values, and (2) the index where each value was in the
% original (unsorted) array
%
% for instance, in this case:
% old_indices_in_B_column_3(1) is 2, which tells you that element #2 (-112) in column 3 of B is the smallest
% old_indices_in_B_column_3(2) is 9, which tells you that element #9 (-70) in column 3 of B is the next smallest
% etc.


%and i can change 'y','in' to another chracters right?

% yes, you can use any valid variable name, or use ~ if you don't need that
% output, e.g., [~,idx] = sort(B(:,3));

[Ann Lee]

thank you!!

Answer 2

[Riccardo Scorretti]

rand('seed',345);
B = randi([-150,300], 10, 7);
[y,in] = sort(B(:,3));

You are sorting a column vector (= the 3rd column of B). The output are:

• y = sorted vector
• in = index such that y = B(in,3)

y'

ans = 1×10

-112 -70 -40 41 68 78 166 170 200 221

B(in,3)'

ans = 1×10

-112 -70 -40 41 68 78 166 170 200 221

It doen't matter whether you are sorting a column vector, a matrix of whatever: ask for two output arguments if you need to know the index (sometimes it is an important information).

[Ann Lee]

thank you!!!