How to sum all values of a column of in a data.frame?

To solve how to sum a column in r you should put all values in a column of a data frame then use the sum() function from the base package as follows:

sum(people$Weight, na.rm = TRUE) 
#na.rm = TRUE will remove all 'NA' values in the column
For example:
df <- data.frame(p=c(10,8,7,3,2,6,7,8),
                  v=c(100,300,150,400,450,250,150,400))
> df
   p   v
1 10 100
2  8 300
3  7 150
4  3 400
5  2 450
6  6 250
7  7 150
8  8 400
sum(df$p, na.rm = TRUE)
[1] 51
Note - you can get built-in help by using ?sum, ?colSums, etc. (by the way, colSums will give you the sum for each column).