R dtplyr select.dtplyr_step 使用名稱對列進行子集化

# S3 method for dtplyr_step
select(.data, ...)

library(dplyr, warn.conflicts = FALSE)

dt <- lazy_dt(data.frame(x1 = 1, x2 = 2, y1 = 3, y2 = 4))

dt %>% select(starts_with("x"))
#> Source: local data table [1 x 2]
#> Call:   `_DT36`[, .(x1, x2)]
#> 
#>      x1    x2
#>   <dbl> <dbl>
#> 1     1     2
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results
dt %>% select(ends_with("2"))
#> Source: local data table [1 x 2]
#> Call:   `_DT36`[, .(x2, y2)]
#> 
#>      x2    y2
#>   <dbl> <dbl>
#> 1     2     4
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results
dt %>% select(z1 = x1, z2 = x2)
#> Source: local data table [1 x 2]
#> Call:   `_DT36`[, .(z1 = x1, z2 = x2)]
#> 
#>      z1    z2
#>   <dbl> <dbl>
#> 1     1     2
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results