如何在R的多年事件表格中标记事件及提取变量首次出现？

Hey there! Let's work through your two questions using your sample data—super straightforward once you break it down. First, let's build the sample data frame we'll use:

# Create the sample data frame
events <- c('event1', 'event1', 'event1', 'event1', 'event1', 'event2', 'event2', 'event2')
years <- c('2000', '2001', '2002', '2003', '2004', '1994', '1995', '1996')
variable1 <- c('False', 'False', 'False', 'True', 'True', 'False', 'False', 'True')
df <- data.frame(events, years, variable1, stringsAsFactors = FALSE)

To flag the first occurrence of each event, we can use grouping operations. The dplyr package makes this intuitive, but I'll also include a base R alternative if you prefer not to load extra packages.

Using dplyr #

library(dplyr)

# Add a column to mark the first row of each event group
df <- df %>%
  group_by(events) %>%
  mutate(is_first_event = row_number() == 1) %>%
  ungroup()

# Check the result
print(df)

This will output:

# A tibble: 8 × 4
  events years variable1 is_first_event
  <chr>  <chr> <chr>     <lgl>         
1 event1 2000  False     TRUE          
2 event1 2001  False     FALSE         
3 event1 2002  False     FALSE         
4 event1 2003  True      FALSE         
5 event1 2004  True      FALSE         
6 event2 1994  False     TRUE          
7 event2 1995  False     FALSE         
8 event2 1996  True      FALSE         

Using Base R #

If you want to stick to base R, use the ave() function to check for the first row in each group:

df$is_first_event_base <- ave(seq_along(df$events), df$events, FUN = function(x) x == min(x))

I'll cover two common scenarios here, since "首次出现" could mean two things: the first instance of the variable in the event group, or the first time the variable hits a specific value (like True in your sample).

Scenario 1: Extract the first instance of the variable (first row of each event) #

This pulls the very first row for each event, which gives you the initial value of variable1 for that event:

first_variable_instance <- df %>%
  group_by(events) %>%
  slice(1) %>%
  ungroup()

print(first_variable_instance)

Output:

# A tibble: 2 × 4
  events years variable1 is_first_event
  <chr>  <chr> <chr>     <lgl>         
1 event1 2000  False     TRUE          
2 event2 1994  False     TRUE          

Scenario 2: Extract the first time the variable hits a specific value (e.g., variable1 = 'True') #

If you want the first row where variable1 becomes True for each event, use this:

first_true_instance <- df %>%
  group_by(events) %>%
  filter(variable1 == 'True') %>%
  slice(1) %>%
  ungroup()

print(first_true_instance)

Output:

# A tibble: 2 × 4
  events years variable1 is_first_event
  <chr>  <chr> <chr>     <lgl>         
1 event1 2003  True      FALSE         
2 event2 1996  True      FALSE         

Base R Alternative for Scenario 2 #

# Filter rows where variable1 is True, then keep only the first row per event
true_rows <- df[df$variable1 == 'True', ]
first_true_base <- true_rows[!duplicated(true_rows$events), ]

内容的提问来源于stack exchange，提问作者newhaus94