R - 基于连续行和因子级别构建唯一组

Question

一般来说，只要它们来自数据框中的连续行，我将如何根据相同的因素进行分组？例如，我想从test 得到下面想要的good_output。

test <- data.frame(time = 1:10, letter = c("a","a","a","b","a","a","a","b","b","b"))
bad_output <- test %>% group_by(letter) %>% summarize(mean_time = mean(time))
bad_output
# A tibble: 2 x 2
  letter mean_time
  <fct>      <dbl>
1 a           4   
2 b           7.75

good_output <- data.frame(letter=c("a","b","a","b"), id=c(1,1,2,2), mean_time=c(2,4,6,9))
good_output
  letter id mean_time
1      a  1         2
2      b  1         4
3      a  2         6
4      b  2         9

Answer 1

我们可以通过'信'和'信'上的运行长度ID（rleid来自data.table）进行分组，summarise得到'时间'的mean，创建带有row_number() 的序列列并选择“grp”列

library(dplyr)
library(data.table)
test %>% 
    group_by(letter, grp = rleid(letter))  %>%
    summarise(mean_time = mean(time)) %>%       
    mutate(id = row_number()) %>%
    ungroup %>%
    select(-grp)
# A tibble: 4 x 3
#  letter mean_time    id
#  <fct>      <dbl> <int>
#1 a              2     1
#2 a              6     2
#3 b              4     1
#4 b              9     2