How to loop through table column comparing subsequent records but ignoring zero values?

I would like to ensure subsequent column values (of wind power) only change by 20% per time step, except where there is a zero value. That is, [1am 2am 3am 4am 5am] [100, 200, 250, 0, 100] would become [1am 2am 3am 4am 5am] [100, 120, 144, 0, 100]. However, as soon as the loop reaches a zero, the rest of the column is set to zero, because 20% of zero is zero.

Here is the code I have tried. I just keep getting a list of zeros after reaching the first zero. I think I need logical indexing but can’t work out how to implement it in this instance.

Thank you for all suggestions.

WeatherT2 = readtable('C:\Windyield_data.csv','Delimiter','comma');

head(WeatherT2)

% WeatherT2 is table name.

% WeatherT2.timestamp and WeatherT2.windpower are the column names.

----------------------------------

numRows = height(WeatherT2)

for row = 2 : numRows

if WeatherT2.windpower(row) == 0

WeatherT2.windpower(row+1) = WeatherT2.windpower(row+1);

elseif WeatherT2.windpower(row) > WeatherT2.windpower(row-1)*1.2

WeatherT2.windpower(row) = WeatherT2.windpower(row-1)*1.2;

else WeatherT2.windpower(row) <= WeatherT2.windpower(row-1)*1.2

WeatherT2.windpower(row) = WeatherT2.windpower(row);

end

end

----------------------------------

numRows = height(WeatherT2)

for row = 2 : numRows

if WeatherT2.windpower(row) > 0

if WeatherT2.windpower(row) > WeatherT2.windpower(row-1)*1.2

WeatherT2.windpower(row) = WeatherT2.windpower(row-1)*1.2;

end

end

end

----------------------------------

numRows = height(WeatherT2)

for row = 2 : numRows

while WeatherT2.windpower(row) ~= 0

if WeatherT2.windpower(row) > WeatherT2.windpower(row-1)*1.2

WeatherT2.windpower(row) = WeatherT2.windpower(row-1)*1.2;

end

break

end

end

----------------------------------

numRows = height(WeatherT2)

for row = 2 : numRows

if WeatherT2.windpower(row) > WeatherT2.windpower(row-1)*1.2

WeatherT2.windpower(row) = WeatherT2.windpower(row-1)*1.2;

else

WeatherT2.windpower(row) =0

break

end

end

----------------------------------

skipNum = [WeatherT2.windpower ~= 0];

numRows = height(WeatherT2)

for row = 2 : numRows

if ismember(row,skipNum) %if row is member of the skipNum array

if WeatherT2.windpower(row) > WeatherT2.windpower(row-1)*1.2

WeatherT2.windpower(row) = WeatherT2.windpower(row-1)*1.2;

end

end

end

Answer 1

[Divyanshu]

Hi Diane,

According to the description provided, here are few assumptions that I have made:

• If current value is 0 in the column, then the subsequent value should not be changed.
• In each iteration the new value of current row is 120% of the previous row value and has nothing to do with the old value of current row.

Here is a demo script you can refer to, and feel free to modify it according to your use case:

windpower = [100 200 250 0 80 130 150]';
iszero = windpower == 0;
numRows = height(windpower);
for i=2:numRows
    if(~iszero(i-1))
        if(~iszero(i))
            windpower(i) = windpower(i-1)*1.2;
        end
    end
end