如何在R语言中为数据框特定值生成递增序列？

Hey there! Let's tackle this R problem you've got. You want to label each consecutive block of 1s in your var column with sequential numbers (1, 2, 3...) while leaving all 0s as 0. Here are a couple of reliable ways to do this:

Method 1: Base R (No External Packages) #

This uses R's built-in rle() (run-length encoding) function, which is perfect for identifying consecutive value blocks:

# Your initial data frame
df <- data.frame(var = c(0,0,1,1,0,0,0,1,1,0,0,0,0,1,1))

# Step 1: Get run-length encoding of the var column
rle_result <- rle(df$var)

# Step 2: Assign sequential numbers to runs of 1s
# First, find which runs are 1s, then assign 1,2,3... to them
rle_result$values[rle_result$values == 1] <- seq_along(rle_result$values[rle_result$values == 1])

# Step 3: Set all non-1 runs back to 0
rle_result$values[rle_result$values != 1] <- 0

# Step 4: Expand the run-length encoding back to the original length
df$newvar <- inverse.rle(rle_result)

# View the final result
print(df)

How this works: #

• rle() breaks your var column into a list of run lengths and corresponding values (e.g., two 0s, two 1s, three 0s, etc.)
• We replace the value of each 1-run with its position in the sequence of 1-runs (first 1-run becomes 1, second becomes 2, etc.)
• inverse.rle() converts the modified run-length list back into a full column matching your original data frame's length.

Method 2: Tidyverse (dplyr + Optional data.table) #

If you prefer using the tidyverse ecosystem, here's a clean approach. We'll use dplyr for data manipulation, and optionally data.table's rleid() function for simpler consecutive group labeling:

Option 2a: Pure dplyr #

library(dplyr)

df <- df %>%
  # Create a unique ID for each consecutive value block
  mutate(group_id = cumsum(var != lag(var, default = var[1]))) %>%
  # Assign sequential numbers to 1-blocks, 0 otherwise
  mutate(newvar = ifelse(
    var == 1,
    dense_rank(group_id[var == 1])[match(group_id, group_id[var == 1])],
    0
  )) %>%
  # Optional: Remove the temporary group_id column
  select(-group_id)

Option 2b: dplyr + data.table (Simpler) #

rleid() from data.table directly generates IDs for consecutive value blocks, making the code more concise:

library(dplyr)
library(data.table)

df <- df %>%
  # Generate consecutive group IDs
  mutate(group_id = rleid(var)) %>%
  # Label 1-blocks sequentially, set 0s to 0
  mutate(newvar = case_when(
    var == 1 ~ as.integer(factor(group_id, levels = unique(group_id[var == 1]))),
    TRUE ~ 0L
  )) %>%
  select(-group_id)

Final Result #

Both methods will produce this desired data frame:

var newvar
1    0      0
2    0      0
3    1      1
4    1      1
5    0      0
6    0      0
7    0      0
8    1      2
9    1      2
10   0      0
11   0      0
12   0      0
13   0      0
14   1      3
15   1      3

内容的提问来源于stack exchange，提问作者adl