r - 使用不存在的列名对数据框进行子集

Question

我在 R 中有这行代码:

newDF <-oldDF[subsettingColumns]

subsettingColumns有几个列名可能存在也可能不存在于 oldDF .如果它不存在，我想在 newDF 中插入一列与 NA 在同一位置的。我如何让它在 R 中工作？

Answer 1

让我们举个例子:

df <- data.frame(a = c(1, 2, 3, 4), b = c(4, 5, 6, 7))
df

#  a b
#1 1 4
#2 2 5
#3 3 6
#4 4 7

#Columns to take subset of
subsettingColumns <- c('a', 'd', 'e')

#Columns which are already present
cols <- subsettingColumns[subsettingColumns %in% names(df)]

#Add them in the new dataframe
newdf <- df[cols]

#Assign NA to the columns which are not defined in the original dataframe
newdf[setdiff(subsettingColumns, cols)] <- NA

newdf
#  a  d  e
#1 1 NA NA
#2 2 NA NA
#3 3 NA NA
#4 4 NA NA