如何根据列值添加数字序列？

Question

I have a data frame that roughly looks like the following:

id data 
1  a
2  b
X  c
3  d
4  e
5  f
X  g
6  h
7  i

I would like the add a 'count' column that repeats the value 1 up until the row that has an ID = 'x', before repeating the value 2 and so on.

Essentially, it would look something like:

id data count
1  a    1
2  b    1
X  c    2
3  d    2
4  e    2
5  f    2
X  g    3
6  h    3
7  i    3

Any advice would be appreciated thanks!

Answer 1

An easier option is cumulative sum on the logical vector where we check the presence of 'X' in the 'id' column

df1$count <- 1 + cumsum(df1$id == "X") 
df1$count
#[1] 1 1 2 2 2 2 3 3 3

data

df1 <- structure(list(id = c("1", "2", "X", "3", "4", "5", "X", "6", 
"7"), data = c("a", "b", "c", "d", "e", "f", "g", "h", "i")), 
class = "data.frame", row.names = c(NA, 
-9L))

Answer 2

Just simply create a counter and use it as column value in a loop, considering you called it "db":

### start counter
count <- 1
### for each DB row
for (i in 1:nrow(db)) {
  ### if ID value = X increase count
  if (db[i,1] == "X") count<- count+1
  ### put count as "count" column value for the row
  db[i,"count"] <- count
}