sum cells of certain columns for each row

问题

I would like to calculate sums for certain columns and then apply this summation for every row. Unfortunately, I can only get to the first step. How do I now make it happen for each row? I know that R doesn't need loops; what are good approaches?

My matrix (zscore) looks like this:

   a    b    c    t   y
1  3    4    7    7   4

2  4    56   6    6   4

3  3    3    2    1   7

4  3    88   9    9   9

Now I would want to calculate the row sum for each row, based on some of the columns. For one row it could look like this:

f1 <- sum(zscore[1,1:2], zscore[1,3], zscore[1,5])

How do I do that now for each row?

回答1:

You could do something like this:

summed <- rowSums(zscore[, c(1, 2, 3, 5)])

回答2:

If you don't have NA you can apply this

suma.zscore = (zscore$a + zscore$c + zscore$t + zscore$y)

来源：https://stackoverflow.com/questions/13482532/sum-cells-of-certain-columns-for-each-row