Calculating mean for a set of columns in jsl
I have a set of column names in a list called list_1, now I want to calculate the mean for each column, but the thing is I do not want to include all the rows in the column when calculating the mean, i have another pre-defined variable that selects specific rows. How do I calculate the mean of the column by selecting the specified rows instead of stepping down through all the rows?for example i wa...