dplyr 变异替换行子集上的几列

(2)只需覆盖(1)指定的输入条件(3)即可维护(not):

1a) mutate_cond为可以合并到管道中的数据帧或数据表创建一个简单函数.此函数类似于mutate，但仅作用于满足条件的行:

mutate_cond <- function(.data, condition, ..., envir = parent.frame()) {
  condition <- eval(substitute(condition), .data, envir)
  .data[condition, ] <- .data[condition, ] %>% mutate(...)
  .data
}

DF %>% mutate_cond(measure == 'exit', qty.exit = qty, cf = 0, delta.watts = 13)

1b) mutate_last This is an alternative function for data frames or data tables which again is like mutate but is only used within group_by (as in the example below) and only operates on the last group rather than every group. Note that TRUE > FALSE so if group_by specifies a condition then mutate_last will only operate on rows satisfying that condition.

mutate_last <- function(.data, ...) {
  n <- n_groups(.data)
  indices <- attr(.data, "indices")[[n]] + 1
  .data[indices, ] <- .data[indices, ] %>% mutate(...)
  .data
}


DF %>% 
   group_by(is.exit = measure == 'exit') %>%
   mutate_last(qty.exit = qty, cf = 0, delta.watts = 13) %>%
   ungroup() %>%
   select(-is.exit)

2) factor out condition通过使其成为一个额外的列，然后将其移除，从而计算出该条件.然后使用ifelse、replace或算术与逻辑，如图所示.这也适用于数据表.

library(dplyr)

DF %>% mutate(is.exit = measure == 'exit',
              qty.exit = ifelse(is.exit, qty, qty.exit),
              cf = (!is.exit) * cf,
              delta.watts = replace(delta.watts, is.exit, 13)) %>%
       select(-is.exit)

3) sqldf我们可以通过管道中的sqldf包使用SQL update来处理数据帧(但不能使用数据表，除非我们转换它们——这可能代表dplyr中的一个缺陷.参见dplyr issue 1579).由于update的存在，我们似乎不希望修改这段代码中的输入，但事实上update作用于临时生成的数据库中输入的副本，而不是实际输入.

library(sqldf)

DF %>% 
   do(sqldf(c("update '.' 
                 set 'qty.exit' = qty, cf = 0, 'delta.watts' = 13 
                 where measure = 'exit'", 
              "select * from '.'")))

4) row_case_when还可以查看中定义的row_case_when

library(dplyr)

DF %>%
  row_case_when(
    measure == "exit" ~ data.frame(qty.exit = qty, cf = 0, delta.watts = 13),
    TRUE ~ data.frame(qty.exit, cf, delta.watts)
  )

Note 1:我们用这个作为DF

set.seed(1)
DF <- data.frame(site = sample(1:6, 50, replace=T),
                 space = sample(1:4, 50, replace=T),
                 measure = sample(c('cfl', 'led', 'linear', 'exit'), 50, 
                               replace=T),
                 qty = round(runif(50) * 30),
                 qty.exit = 0,
                 delta.watts = sample(10.5:100.5, 50, replace=T),
                 cf = runif(50))

Note 2: dplyr第134、631、1518和1573期中也讨论了如何轻松指定更新行子集的问题，其中631是主线，1573是对这里答案的回顾.