按组查找运行最大值

Question

我需要使用R按组查找变量的运行最大值.变量按组内的时间排序使用df[order(df$group, df$time),].

我的变量有一些NA,但我可以通过用零替换它来处理它.

这是数据框df的样子:

(df <- structure(list(var = c(5L, 2L, 3L, 4L, 0L, 3L, 6L, 4L, 8L, 4L),
               group = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L),
                                 .Label = c("a", "b"), class = "factor"),
               time = c(1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L, 5L)),
          .Names = c("var", "group","time"),
          class = "data.frame", row.names = c(NA, -10L)))

#    var group time
# 1    5     a    1
# 2    2     a    2
# 3    3     a    3
# 4    4     a    4
# 5    0     a    5
# 6    3     b    1
# 7    6     b    2
# 8    4     b    3
# 9    8     b    4
# 10   4     b    5

我想要一个变量curMax:

var  |  group  |  time  |  curMax
5       a         1         5
2       a         2         5
3       a         3         5
4       a         4         5
0       a         5         5
3       b         1         3
6       b         2         6
4       b         3         6
8       b         4         8
4       b         5         8

如果您有任何想法如何在R中实现它,请告诉我.

Answer 1

我们可以试试data.table.将'data.frame'转换为'data.table'(setDT(df1)),按'group'分组,我们得到cummax'var'并将:=它()分配给一个新变量('curMax')

library(data.table)
setDT(df1)[, curMax := cummax(var), by = group]

正如@Michael Chirico评论的那样,如果数据不是order'时间',我们可以在'i'中做到这一点

setDT(df1)[order(time), curMax:=cummax(var), by = group]

或者 dplyr

library(dplyr)
df1 %>% 
    group_by(group) %>%
    mutate(curMax = cummax(var)) 

如果df1是tbl_sql显式排序可能需要,使用arrange

df1 %>% 
    group_by(group) %>%
    arrange(time, .by_group=TRUE) %>%
    mutate(curMax = cummax(var)) 

要么 dbplyr::window_order

library(dbplyr)

df1 %>% 
    group_by(group) %>%
    window_order(time) %>%
    mutate(curMax = cummax(var)) 

Answer 2

你可以这样做：

df$curMax <- ave(df$var, df$group, FUN=cummax)