r - 在data.table r中按名称选择非连续列

Question

我的磁盘上有数据库，我想使用 : 选择多个列，偶尔在 data.table 中使用列名。

以前的答案只包括使用索引进行列选择，这对我的情况来说是不可取的。

例子如下:

library(gapminder)
data(gapminder)
setDT(gapminder)

names(gapminder) # [1] "country"   "continent" "year"      "lifeExp"   "pop"       "gdpPercap"

# I would like to select columns from `country` to `year` and pop

gapminder[,country:year] # this one works



gapminder[,country:year + pop] # doesn't work
gapminder[,c(country:year,pop)] # doesn't work either

gapminder[,.SD, .SDcols = c(country:year,pop)] # doesn't work

我正在为这个问题挠头。我将不胜感激任何建议。

Answer 1

另一种选择:

gapminder[, c(.SD, .(pop=pop)), .SDcols=country:year] 

或者如果你有更多列，

cols <- setNames(c("pop", "lifeExp"), c("pop", "lifeExp"))
gapminder[, c(.SD, mget(cols)), .SDcols=country:year] 

输出:

          country continent year      pop lifeExp
   1: Afghanistan      Asia 1952  8425333  28.801
   2: Afghanistan      Asia 1957  9240934  30.332
   3: Afghanistan      Asia 1962 10267083  31.997
   4: Afghanistan      Asia 1967 11537966  34.020
   5: Afghanistan      Asia 1972 13079460  36.088
  ---                                            
1700:    Zimbabwe    Africa 1987  9216418  62.351
1701:    Zimbabwe    Africa 1992 10704340  60.377
1702:    Zimbabwe    Africa 1997 11404948  46.809
1703:    Zimbabwe    Africa 2002 11926563  39.989
1704:    Zimbabwe    Africa 2007 12311143  43.487