Storing results of each column-operation in seperate row in pig - apache-pig

Question

I need to perform some numerical operations (using a UDF) on every column of my table. And for every column I am getting 2 values (mean and standard-dev). But the final result is coming like (mean_1, sd_1, mean_2, sd_2, mean_3, sd_3...), where 1,2... are column indexes. But I need the output for every column in a separate row. Like:
mean_1, sd_1 \\for col1
mean_2, sd_2 \\for col2
...
Here is the pig script I'm using:
data = LOAD 'input_file.csv' USING PigStorage(',') AS (C0,C1,C2);
grouped_data = GROUP data ALL;
res = FOREACH grouped_data GENERATE FLATTEN(data), AVG(data.$1) as mean, COUNT(data.$1) as count;
tmp = FOREACH res {
diff = (C1-mean)*(C1-mean);
GENERATE *,diff as diff;
};
grouped_diff = GROUP tmp all;
sq_tmp = FOREACH grouped_diff GENERATE flatten(tmp), SUM(tmp.diff) as sq_sum;
stat_tmp = FOREACH sq_tmp GENERATE mean as mean, sq_sum/count as variance, SQRT(sq_sum/count) as sd;
stats = LIMIT stat_tmp 1;
Could anybody please guide me on how to achieve this?

Answer 1

Thanks. I got the required output by creating tuples of mean and sd values for respective columns and then storing all such tuples in a bag. Then in the next step I flattened the bag.
tupled_stats = FOREACH raw_stats generate TOTUPLE(mean_0, var_0, sd_0) as T0, TOTUPLE(mean_1, var_1, sd_1) as T1, TOTUPLE(mean_2, var_2, sd_2) as T2;
bagged_stats = FOREACH tupled_stats generate TOBAG(T0, T1, T2) as B;
stats = foreach bagged_stats generate flatten(B);