在数据框中重复行并添加增量字段[重复]

Question

我找到了很多关于如何复制记录的答案，但我还想为每条重复记录添加一个增量字段。我发现了一个类似的问题，但他们没有 startValue 字段：Repeat the rows in a data frame based on values in a specific column。

我的数据框以

开头

df <-
  data startValue freq
    a        3.4    3
    b        2.1    2
    c        6.3    1

我想要这个输出

df.expanded <-
    data startValue value
       a        3.4     3
       a        3.4     4
       a        3.4     5
       b        2.1     2
       b        2.1     3
       c        6.3     6

我确实找到了一种方法来做到这一点，但我想要一些更简单的方法，可以很好地处理大型数据集。这就是我所做的。

df <- data.frame(data = c("a", "b", "c"),
                 startValue = c(3.4, 2.1, 6.3),
                 freq = c(3,2,1))
df

# find the largest integer that I will need as an index.
n <- floor(max(df$startValue + df$freq))-1

# repeat each df record n times. Only the record with the
# largest startValue + freq needs to be repeated this many
# times, but I am repeating everything this many times.
df.expanded <- df[rep(row.names(df), each = n), ]

# Use recycling to fill a new column. Now I have created
# a Cartesian product. If n is 46, records with a
# freq of 46 are repeated just the right number of times.
# but records with a freq of 2 are repeated many more times
# than is needed.
df.expanded$value <- 1:n

# finally, I filter out all the extra repeats that I didn't need.
df.expanded <-
df.expanded[df.expanded$value >= floor(df.expanded$startValue)
            & df.expanded$value < floor(df.expanded$startValue+df.expanded$freq),]
df.expanded[-3]

有没有一种方法可以更好地处理大型数据集？大多数记录需要少于 5 次重复，但少数需要 50 次重复。当 10000 条记录中只有 1 条需要大量重复时，我不喜欢将所有内容重复 50 次的想法。谢谢。

Answer 1

您可以从tidyr 使用uncount

library(dplyr)
library(tidyr)

df %>%
  uncount(weights = freq, .id = "n", .remove = F) %>%
  mutate(value = freq + n - 1)

  data startValue freq n value
1    a        3.4    3 1     3
2    a        3.4    3 2     4
3    a        3.4    3 3     5
4    b        2.1    2 1     2
5    b        2.1    2 2     3
6    c        6.3    1 1     1

Answer 2

我不知道你为什么想要这样，但使用 tidyverse ：

df %>% 
  mutate(value = map(freq,~.:(2*.-1))) %>% 
  unnest %>%
  select(-freq)
#   data startValue value
# 1    a        3.4     3
# 2    a        3.4     4
# 3    a        3.4     5
# 4    b        2.1     2
# 5    b        2.1     3
# 6    c        6.3     1