Sorting an array of numbers in descending order by using while loop

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Syed Shahed
Syed Shahed 2020-5-4
评论： Guillaume 2020-5-4
I wrote the code to sort number in descending order but my code failed to do so (actually i was the failure lol).
Example: Consider, the given array is x=[4 6 9 2 5 0 1] and i want the output y as [9 6 5 4 2 1 0].
What is more, my thinking was like that in seq-
1) Find maximum number from a given array
2) Then use find function to detect the maximum element idexing
3) And then remove the maximum number from the array and reducing the array length
However, i am successfully failed to do what i am looking for. I am determined to use only the while loop to execute this code (nothing else is appreciable e.g sort function and for loop)
Can anyone tell me where i did wrong while i was writing the code? i mean the erroneous part of the code.
I will be glad if any expert give me an advice or suggestion to correct the the code.
function y =sortingnumsindes(x)
y=[];
while(numel(x)>0)
y=max(x);
p=find(x==y);
x(p)=[];
end
y=x;
end

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采纳的回答

David Hill
David Hill 2020-5-4
function y =sortingnumsindes(x)
y=[];
while(numel(x)>0)
m=max(x);
p=find(x==m,1);%need ,1 to handle any duplicates
x(p)=[];
y=[y,m];%needed to store each subsequent element in array y
end
end
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Syed Shahed
Syed Shahed 2020-5-4
Thanks brother , you get the point . Actually i am a newbie and sometimes face some awkward problems thats why need a clear view to understand what happening inside . And David doing really well .
Guillaume
Guillaume 2020-5-4
As my comment seems to be a bit controversial here is some additional reason why I initially wrote it:
There are several steps to writing code. There's first figuring out that algorithm, already there's a problem with the algorithm written, it's missing a step where the maximum is appended to the output. Then there's translating that algorithm into code, and here there was several issue. Then there's the debugging part and understanding where it's gone wrong. In my opinion, in order to get better at coding you need to go through all these steps yourself. Here in particular, Syd needed to understand that y was used for two different things and that he actually never went through the missing step of storing the elements that are removed.
So, I'm afraid the "clear view to understand what happening inside" can only come through a process of trial and error, not by having the solution handed directly to you.

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更多回答（1 个）

Guillaume
Guillaume 2020-5-4
"1) Find maximum number from a given array"
"2) Then use find function to detect the maximum element idexing"
Have a look at the documentation of max, in particular the 2nd output which is exactly the index you want.
p=find(x==y);
will work in your code as long as there's only one value equal to the max. If there's more than one, p is a vector of indices and you'll end up deleting too many elements.
y=[];
%...
y=max(x);
%...
y=x;
You need to rethink what y is, you're using it for two purpose, and how you fill it.

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