Yes, row wise mean! But the columns are not in series as you said. So, I couldn't use ":" operator, like "1:3". Let's say, there are ten columns. I want to calculate the row wise mean of Col 3, 6 and 9. Also, I want to calculate the row wise mean of the columns Col 1,2,4,5,7, and 8. Something like that.
Mean 1 = (Col 3 + Col 6 + Col 9)/3
Mean 2 = (Col 1 + Col 2 + Col 4 + Col 5 + Col 7 + Col 8)/6
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Mean n = ...