有条件地选择dplyr中的列 [英] Select columns in dplyr conditionally

问题描述

library(nycflights13)
library(dplyr)

head(flights)

id.vec <- c("a", "b", "c")

for(i in seq_along(id.vec)){

  id <- id.vec[i]

  temp <- flights %>% dplyr::select(year, day, dep_time, arr_time) %>%
                      dplyr::mutate(year = year - mean(year),
                                    day = day - mean(day),
                                    dep_time = dep_time - mean(dep_time),
                                    arr_time = arr_time - mean(arr_time))

  # do some other tasks with temp file
}

做其他任务我的问题是我该如何放置一个条件，如果 id == c ，则不要
选择 dep_time 列，然后不要执行 dep_time = dep_time-mean（dep_time）

My question is how can I put a condition that if id == "c", then do not select the dep_time column and also do not execute the dep_time = dep_time - mean(dep_time)

推荐答案

一个简单的选择是在for循环中包含if ... else ...语句：

A simple option would be to include an if... else... statement in the for loop:

for(i in seq_along(id.vec)){


  id <- id.vec[i]

  if(id == 'c') {
  temp <- flights %>% dplyr::select(year, day, arr_time) %>%
    dplyr::mutate(year = year - mean(year),
                  day = day - mean(day),
                  arr_time = arr_time - mean(arr_time))
  } else {
    temp <- flights %>% dplyr::select(year, day, dep_time, arr_time) %>%
      dplyr::mutate(year = year - mean(year),
                    day = day - mean(day),
                    dep_time = dep_time - mean(dep_time),
                    arr_time = arr_time - mean(arr_time))
  }

  # do some other tasks with temp file
}

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