Q:

Removing offsetting rows in a tibble

Please note that the order of the data and the VALUE column are different from my prior question. How do I remove offsetting rows in a tibble?  The accepted answer for the question works for the data set I provided, however changing values causes the answer to fail. 
I am trying to remove rows that have offsetting values. 
library(dplyr)
a <- c(1, 1, 1, 1, 2, 2, 2, 2,2,2)
b <- c("a", "b", "b", "b", "c", "c","c", "d", "d", "d")
d <- c(10, 10, -10, 50, 20, -20, 60, 30, -30, 70)
o <- c("A", "B", "C", "D", "E", "F", "G", "H", "I", "J")
df <- tibble(ID = a, SEQ = b, VALUE = d, OTHER = o)

Generates this ordered table that is grouped by ID and SEQ.
> df
# A tibble: 10 x 4
      ID   SEQ VALUE OTHER
   <dbl> <chr> <dbl> <chr>
 1     1     a    10     A
 2     1     b   -10     B
 3     1     b    10     C
 4     1     b    50     D
 5     2     c   -20     E
 6     2     c    20     F
 7     2     c    60     G
 8     2     d   -30     H
 9     2     d    30     I
10     2     d    70     J

I want to drop the row pairs (2,3), (5,6), (8,9) because VALUE negates the VALUE in the matching previous row. 
I want the resulting table to be
> df2
# A tibble: 4 x 4
     ID   SEQ VALUE OTHER
  <dbl> <chr> <dbl> <chr>
1     1     a    10     A
2     1     b    50     D
3     2     c    60     G
4     2     d    70     J

I know that I can't use group_by %>% summarize, because I need to keep the value that is in OTHER.  I've looked at the dplyr::lag() function but I don't see how that can help.  I believe that I could loop through the table with some type of for each loop and generate a logical vector that can be used to drop the rows, but I was hoping for a more elegant solution.

A:

Unless I completely misunderstood your question, does this do the job?
idx <- which(diff(cumsum(df$VALUE)) < 0);
df[-c(idx, idx + 1), ];
## A tibble: 4 x 4
#     ID   SEQ VALUE OTHER
#  <dbl> <chr> <dbl> <chr>
#1     1     a    10     A
#2     1     b    50     D
#3     2     c    60     G
#4     2     d    70     J

