Error with find function in a for loop

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Kafayat Olayinka 2020-2-6

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评论： TADA 2020-2-6

Time, height, and temperature variable all have the same array size. I want find temperature at altitude greater than 6km. I also want 6kmtemp to be the same size as temperature. However, after running this code, the result was an empty array. t3 is 0*0. How can I make this find function work in a for loop. BTW, the find function worked when i didnt have it in the loop. However, the array size changed. What am i missing? Thanks

 for i=1:length(Time)
     t3=find(height(i)>=6);
     6kmtemp(i,t3)=temperature(t3);
 end

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Star Strider 2020-2-6

在 MATLAB Online 中打开

Note that:

6kmtemp

is not an acceptable variable name, and will throw an error.

Consider:

temp6km

instead.

Kafayat Olayinka 2020-2-6

That is true. however, that was not the error. After running that code, t3 array is empty. meaning the find function in the loop didn't work.

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TADA 2020-2-6

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Find accepts a logical vector and returns all the indices containing 1.

The problem is you are giving find a scalar value so it's going to return an empty value when height(i) < 6 and 1 whenever height(i) >= 6

Did you consider not using find at all? Instead you can switch to logical indexing:

6kmtemp = nan(size(temperature));
atLeast6km = height >= 6;
6kmtemp(atLeast6km) = temperature(atLeast6km);

You should preallocate 6kmtemp to whatever value you want the "empty" cells to have, I used NaN but you can define your own constants according to what makes sense for you