How to make simpler this at 'if condition'?

Question

CHOI HYUNDUK 2018-12-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/437259-how-to-make-simpler-this-at-if-condition

评论： CHOI HYUNDUK 2018-12-26

采纳的回答： Star Strider

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There is 'a' vector [6x9].

And I want to define 'ahat' depends on 'ii' value.

For example, if ii=3, 'ahat' use a(1,1),a(2,1),a(3,1),a(4,1),a(5,1),a(6,1)] this value.

But could I make simpler this?

if (ii<5)
ahat=[a(1,1),a(2,1),a(3,1),a(4,1),a(5,1),a(6,1)];
elseif ((4<ii)&&(ii<9))
ahat=[a(1,2),a(2,2),a(3,2),a(4,2),a(5,2),a(6,2)]; 
elseif ((8<ii)&&(ii<13))
ahat=[a(1,3),a(2,3),a(3,3),a(4,3),a(5,3),a(6,3)]; 
elseif ((12<ii)&&(ii<17))
ahat=[a(1,4),a(2,4),a(3,4),a(4,4),a(5,4),a(6,4)]; 
elseif ((16<ii)&&(ii<21))
ahat=[a(1,5),a(2,5),a(3,5),a(4,5),a(5,5),a(6,5)]; 
elseif ((20<ii)&&(ii<25))
ahat=[a(1,6),a(2,6),a(3,6),a(4,6),a(5,6),a(6,6)]; 
elseif ((24<ii)&&(ii<29))
ahat=[a(1,7),a(2,7),a(3,7),a(4,7),a(5,7),a(6,7)]; 
elseif ((28<ii)&&(ii<33))
ahat=[a(1,8),a(2,8),a(3,8),a(4,8),a(5,8),a(6,8)]; 
else ((32<ii)&&(ii<37))
ahat=[a(1,9),a(2,9),a(3,9),a(4,9),a(5,9),a(6,9)];
end
a = ahat;

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Answer 1

Star Strider 2018-12-26

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https://ww2.mathworks.cn/matlabcentral/answers/437259-how-to-make-simpler-this-at-if-condition#answer_353966

编辑：Star Strider 2018-12-26

在 MATLAB Online 中打开

I am not certain this is more efficient than your code, however it takes advantage of the repeating patterns to make it simpler:

a = randi(9, 6, 9);                                                 % Create ‘a’
C1 = 4 : 4 : 32;
ahatfcn = @(k) [a(1,k),a(2,k),a(3,k),a(4,k),a(5,k),a(6,k)];         % Create Anonymous Function
for ii = 1 : 40                                                     % Loop Over ‘ii’
    if ii < 5
        ahat = ahatfcn(1);
    else
        for k1 = 1:numel(C1)
            if ((C1(k1)<ii) && (ii<(C1(k1)+5)))
                ahat = ahatfcn(k1+1);
            end
        end
    end
end
a = ahat

It runs without error. I defer to you to determine if it produces the result you want.

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Answer 2

Steven Lord 2018-12-26

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在 MATLAB Online 中打开

Make some sample data.

a = reshape(randperm(6*9), [6 9])
ii = 15;

Define the cutoffs.

vec = [0 4 8 12 16 20 24 28 32 36];
% or
vec = 0:4:36;

Determine which bin your selected ii falls into. For this sample ii, it falls into bin #4 (between 12 and 16.)

d = discretize(ii, vec)

Create ahat.

ahat = a(1:6, d);

This will even work with a row vector ii.

ii = [15 21 28];
d = discretize(ii, vec)
ahat2 = a(1:6, d)

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CHOI HYUNDUK 2018-12-26

Thank you a lot!

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Answer 3

madhan ravi 2018-12-26

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https://ww2.mathworks.cn/matlabcentral/answers/437259-how-to-make-simpler-this-at-if-condition#answer_353957

编辑：madhan ravi 2018-12-26

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a = rand(6,9)  % some data to test
ii = 6 % according to our expectation the result should be the second column
if ii < 5
ahat = a(:,1) ;
elseif ( 4 < ii ) && ( ii < 9 )
ahat = a(:,2) ;
elseif ( 8 < ii ) && ( ii < 13 )
ahat = a(:,3) ;
elseif ( 12 < ii ) && ( ii < 17 )
ahat = a(:,4) ; 
elseif ( 16 < ii ) && ( ii < 21 )
ahat = a(:,5) ; 
elseif ( 20 < ii ) && ( ii < 25 )
ahat = a(:,6) ; 
elseif ( 24 < ii ) && ( ii < 29 )
ahat = a(:,7) ; 
elseif ( 28 < ii ) && ( ii < 33 )
ahat = a(:,8) ; 
else ( 32 < ii ) && ( ii < 37 )
ahat = a(:,9) ;
end
a = ahat.' 

Gives:

a =
  Columns 1 through 7
    0.1672    0.9516    0.5479    0.6663    0.9991    0.1904    0.6448
    0.1062    0.9203    0.9427    0.5391    0.1711    0.3689    0.3763
    0.3724    0.0527    0.4177    0.6981    0.0326    0.4607    0.1909
    0.1981    0.7379    0.9831    0.6665    0.5612    0.9816    0.4283
    0.4897    0.2691    0.3015    0.1781    0.8819    0.1564    0.4820
    0.3395    0.4228    0.7011    0.1280    0.6692    0.8555    0.1206
  Columns 8 through 9
    0.5895    0.6171
    0.2262    0.2653
    0.3846    0.8244
    0.5830    0.9827
    0.2518    0.7302
    0.2904    0.3439
ii =
     6
a =
    0.9516    0.9203    0.0527    0.7379    0.2691    0.4228