R dtplyr unite.dtplyr_step 通过将字符串粘贴在一起将多列合并为一列。

# S3 method for dtplyr_step
unite(data, col, ..., sep = "_", remove = TRUE, na.rm = FALSE)

library(tidyr)

df <- lazy_dt(expand_grid(x = c("a", NA), y = c("b", NA)))
df
#> Source: local data table [4 x 2]
#> Call:   `_DT41`
#> 
#>   x     y    
#>   <chr> <chr>
#> 1 a     b    
#> 2 a     NA   
#> 3 NA    b    
#> 4 NA    NA   
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results

df %>% unite("z", x:y, remove = FALSE)
#> Source: local data table [4 x 3]
#> Call:   setcolorder(copy(`_DT41`)[, `:=`(z = paste(x, y, sep = "_"))], 
#>     c("z", "x", "y"))
#> 
#>   z     x     y    
#>   <chr> <chr> <chr>
#> 1 a_b   a     b    
#> 2 a_NA  a     NA   
#> 3 NA_b  NA    b    
#> 4 NA_NA NA    NA   
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results

# Separate is almost the complement of unite
df %>%
  unite("xy", x:y) %>%
  separate(xy, c("x", "y"))
#> Source: local data table [4 x 2]
#> Call:   copy(`_DT41`)[, `:=`(xy = paste(x, y, sep = "_"))][, `:=`(c("x", 
#> "y"), NULL)][, `:=`(c("x", "y"), tstrsplit(xy, split = "[^[:alnum:]]+"))][, 
#>     `:=`("xy", NULL)]
#> 
#>   x     y    
#>   <chr> <chr>
#> 1 a     b    
#> 2 a     NA   
#> 3 NA    b    
#> 4 NA    NA   
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results
# (but note `x` and `y` contain now "NA" not NA)