如何统计R中某列中某个值的出现次数？

Question

我有以下数据：

df <- data.frame(id = c("1", "1", "1", "1", "2", "2", "2"), 
                 x = c(0, 1, 0, 1, 0, 1, 0))

id x
 1 0
 1 1
 1 0
 1 1
 2 0
 2 1
 2 0

我想统计

1

中

x

的出现次数。所需的输出：

id x count
 1 0     0
 1 1     1
 1 0     0
 1 1     2
 2 0     0
 2 1     1
 2 0     0

我该怎么做？首选

dplyr

解决方案。

Answer 1

library(tidyverse)

df <- tibble(id = c("1", "1", "1", "1", "2", "2", "2"), 
                 x = c(0, 1, 0, 1, 0, 1, 0))

df |> mutate(
  cumsum = cumsum(x),
  tally = if_else(x == 0, 0, cumsum),
  .by = id
  )
#> # A tibble: 7 × 4
#>   id        x cumsum tally
#>   <chr> <dbl>  <dbl> <dbl>
#> 1 1         0      0     0
#> 2 1         1      1     1
#> 3 1         0      1     0
#> 4 1         1      2     2
#> 5 2         0      0     0
#> 6 2         1      1     1
#> 7 2         0      1     0

^{创建于 2023-11-04，使用 reprex v2.0.2}

Answer 2

您可以获取

x

值的累积总和。

library(dplyr)

df %>%
  mutate(count = replace(cumsum(x), x == 0, 0), .by = id)

#  id x count
#1  1 0     0
#2  1 1     1
#3  1 0     0
#4  1 1     2
#5  2 0     0
#6  2 1     1
#7  2 0     0