Summarise over all columns

Question

I have data of the following format:

gen = function () sample.int(10, replace = TRUE)
x = data.frame(A = gen(), C = gen(), G = gen(), T = gen())

Answer 1

I once did something similar, and by that time I ended up with:

x %>%
  rowwise() %>%
  do(data.frame(., res = sum(unlist(.))))
#    A  C G  T res
# 1  3  2 8  6  19
# 2  6  1 7 10  24
# 3  4  8 6  7  25
# 4  6  4 7  8  25
# 5  6 10 7  2  25
# 6  7  1 2  2  12
# 7  5  4 8  5  22
# 8  9  2 3  2  16
# 9  3  4 7  6  20
# 10 7  5 3  9  24

---

Perhaps your more complex function works fine without unlist, but it seems like it is necessary for sum. Because . refers to the "current group", I initially thought that . for e.g. the first row in the rowwise machinery would correspond to x[1, ], which is a list, which sum swallows happily outside do

is.list((x[1, ]))
# [1] TRUE

sum(x[1, ])
# [1] 19 

However, without unlist in do an error is generated, and I am not sure why:

x %>%
  rowwise() %>%
  do(data.frame(., res = sum(.)))
# Error in sum(.) : invalid 'type' (list) of argument