sum() with conditions provides incorrect result in dplyr package

Question

When applying sum() with conditions in summarize() function, it does not provide the correct answer.

Make a data frame x:

x = d         


        

Answer 1

Duplicate names are causing you problems. In this code

x %>% summarize(val = sum(val), val.2 = sum(val[flag == 2]))

You have two val objects. One created from val = sum(val) and other from the data frame x. In your code, you change val from the data frame value to val=sum(val) = 5. Then you do

`val[flag == 2]`

which gives a vector c(2, NA), since val = 5. Hence, when you add 2 + NA you get NA. The solution, don't use val twice,

x %>% summarize(val_sum = sum(val), val.2 = sum(val[flag == 2]))