How could I get RMSE and MAE for each repeat

[xiangpang]

Hello,

I want to calculate RMSE and MAE. With data data4rmse I could get one RMSE and MAE using following code.

Now I have data EQ with repeating the experiment for 3 times. How could I get RMSE and MAE for each repeat and output them into one table? 

Thanks

data data4rmse;
input ID bmi dm bmi_me;
cards;
1 13 40 8
2 13 29 37
3 30 14 25
4 38 38 23
;
run;
	data rmse;
    retain square_error_sum abs_error_sum; 
    set data4rmse 
        end=last /* Flag for the last observation */
        ;
    error = BMI - BMI_me; /* Calculate simple error */
    square_error = error * error; /* error^2 */
    if _n_ eq 1 then do;
        /* Initialize the sums */
        square_error_sum = square_error; 
        abs_error_sum = abs(error); 
        end;
    else do;
        /* Add to the sum */
        square_error_sum = square_error_sum + square_error; 
        abs_error_sum = abs_error_sum + abs(error);
    end;
    if last then do;
        /* Calculate RMSE and MAE and store in SAS data set. */
        mae = abs_error_sum/_n_;
        rmse = sqrt(square_error_sum/_n_); 
        end;
run;

data eq;
input repeat ID bmi dm bmi_me;
cards;
1 1 13 40 8
1 2 13 29 37
1 3 30 14 25
1 4 38 38 23
2 1 30 45 19
2 2 30 20 14
2 3 67 13 14
2 4 13 27 13
3 1 33 23 46
3 2 13 12 56
3 3 13 13 34
3 4 13 45 13
;
run;

[s_lassen · Accepted solution]

Something like this, perhaps?

data rmse;
  square_error_sum = 0; 
  abs_error_sum = 0; 
  do n=1 by 1 until(last.repeat);
    set eq;
    by repeat;
    error = BMI - BMI_me; /* Calculate simple error */
    square_error = error * error; /* error^2 */
    square_error_sum + square_error; 
    abs_error_sum + abs(error); 
    end;
  /* Calculate RMSE and MAE and store in SAS data set. */
  mae = abs_error_sum/n;
  rmse = sqrt(square_error_sum/n);
  keep repeat mae rmse n;
run;

I assumed that you only really wanted one row for each repeat. I included the count (n), in case you have a different number of observations in each repeat.

The statement "a+b;" is called a SUM statement, it is equivalent to "retain a 0; a=sum(a,b);", which can save you a lot of coding.

[xiangpang]

Thanks for your teaching and code. I am happy to learn it. 

Thanks again.