Question

我想添加一个“数字滞后”的新列，但如果组发生更改，我不想将之前的组作为滞后数字。这使用ifelse显示如下，但是如何使用apply（）？

执行此操作

mydata=data.frame(groups = c("A","A","B","B"), numbers= c(1,2,3,4))
mydata$numbers_lagged = lag(mydata$numbers, k=1)  
mydata$groups_lagged= lag(mydata$groups, k=1) 
mydata$numbers_lagged= ifelse(mydata$groups != mydata$groups_lagged,NA, mydata$numbers_lagged) #if the group does not equal the previous group then set to NA
mydata

Answer 1

与apply比较我建议在group_by

中使用dplyr

library(dplyr)
mydata%>%group_by(groups)%>%dplyr::mutate(numbers_lagged=lag(numbers))%>%
   ungroup()%>%
   arrange(groups)%>%
   mutate(groups_lagged=lag(groups))

  groups numbers numbers_lagged groups_lagged
  <fctr>   <dbl>          <dbl>        <fctr>
1      A       1             NA            NA
2      A       2              1             A
3      B       3             NA             A
4      B       4              3             B

应用函数来访问不同列的先前值

1 个答案: