I have a homework to do and my professor won't let me use the command For in it, someone can help me?
How to sum values from columns of a matrix into a vector tha concatenates sum of each column? (Without using For)
Try using the function colSums, which is in base R - you don't need to install any package to use it.
forgive my inexperience, I think I wrote what I want to do in a wrong way. I want to sum the values of the first and second row of a matrix and get a vector as output, and each value of the vector is the sum of the column 1 of these two lines, and after column 2, and goes on. maybe rowsum can help me?
Oh, I got it now, colSums does help me with that, but I'm trying to find way to stop it at row 2
Can you use the matrix below to give an example of what you're trying to calculate? I want to make sure that I understand what you're asking.
> m <- matrix(1:9, nrow = 3) > m [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9
Yes, using this matrix I would like to sum the values of the first and second row and get as a result the vector:
3 9 15
You can definitely use colSums to do this. You need to think about how you can select just the first two rows of a matrix - you can apply colSums to the result.
I got it now, thank you for helping.
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