统计重复项的数量,并将其放入数据帧中的一列中

df$count <- with(df, ave(rep(1, nrow(df)), b, a, FUN = cumsum))

试试这个:

df$count = sequence(rle(df$a)$lengths)
df

我们可以用 data.table

library(data.table)
setDT(df)[, count := seq_len(.N), .(a, b)]
df
#    a b count
#1: 1 A     1
#2: 1 A     2
#3: 2 C     1
#4: 3 C     1
#5: 4 D     1
#6: 4 D     2

我有一个类似的问题,但只需要根据1列中的信息计算重复项。user7298145的回答在小数据帧中效果很好,但我的数据有20k行,失败了,出现了错误:

Error: memory exhausted (limit reached?)
Error during wrapup: memory exhausted (limit reached?)

所以我创建了一个 for

##  order the values that are duplicated
primary_duplicated <- primary_duplicated1[order(primary_duplicated1$md5), ]
##  create blank/NA column
primary_duplicated$count <- NA
##  set first value as 1
primary_duplicated$count[1] <- 1
##  set count of duplicates to 1 greater than the 
##  value of the preceding duplicate
for (i in 2:nrow(primary_duplicated)) {
      if (primary_duplicated$md5[i] == primary_duplicated$md5[i-1]) {
            primary_duplicated$count[i] <- primary_duplicated$count[i-1] + 1
      } else {
      ##  set the count value for the first incidence of
      ##  a duplicate as 1
            primary_duplicated$count[i] <- 1
      }
}