R data.table: Summarize each column with each function and name the new columns automatically

data.table_summaries.R

library(magrittr)
library(data.table)

summaries <- function(dt, col_names, fun_names, additional_code, by, sep='__')
  eval(parse(
    text=
      expand.grid(var=col_names, fun=fun_names) %>% 
      {paste0('`',.$fun,sep,.$var,'`=`',.$fun,'`(',.$var,')')} %>%
      c(additional_code) %>% 
      paste(collapse=',') %>% 
      paste0('dt[,.(',.,'),by=c(',
             by %>% 
               gsub('"','\\"',.,fixed=TRUE) %>%
               paste0('"',.,'"') %>% 
               paste(collapse=','),
             ')]')
  ))


#    #    Examples ---------------------------------------------------------
#    
#    ##    Helpers
#    
#    Sum <- function(x)
#      if (all(is.na(x))) #    if all xs are NA then sum=NA instead of sum=0
#        NA_real_ else sum(x,na.rm=TRUE)
#    
#    Mean <- function(x)
#      mean(x, na.rm=TRUE)
#    
#    Median <- function(x)
#      median(x, na.rm=TRUE)
#    
#    ##    Fake data
#    my_dt <-
#      data.table(A=c('a','a','a', 'b','b','b'),
#                 B=c(1,2,3, 1,2,3),
#                 x=1:6,
#                 y=101:106)
#    my_dt
#    #       A B x   y
#    #    1: a 1 1 101
#    #    2: a 2 2 102
#    #    3: a 3 3 103
#    #    4: b 1 4 104
#    #    5: b 2 5 105
#    #    6: b 3 6 106
#    
#    ##    Usage example:
#    summaries(dt=my_dt,
#              col_names=c('x','y'),
#              fun_names=c('Sum','Mean','Median'),
#              additional_code='Count=length(x)',
#              by=c('A','B'))
#    ##    Generated code:
#    #     dt[,.(`Sum__x`=`Sum`(x),
#    #           `Sum__y`=`Sum`(y),
#    #           `Mean__x`=`Mean`(x),
#    #           `Mean__y`=`Mean`(y),
#    #           `Median__x`=`Median`(x),
#    #           `Median__y`=`Median`(y),
#    #           Count=length(x))
#    #       ,by=c("A","B")]
#    ##    Result:
#    #       A B Sum__x Sum__y Mean__x Mean__y Median__x Median__y Count
#    #    1: a 1      1    101       1     101         1       101     1
#    #    2: a 2      2    102       2     102         2       102     1
#    #    3: a 3      3    103       3     103         3       103     1
#    #    4: b 1      4    104       4     104         4       104     1
#    #    5: b 2      5    105       5     105         5       105     1
#    #    6: b 3      6    106       6     106         6       106     1
#    
#    ##    Another usage example:
#    summaries(dt=my_dt,
#              col_names=c('x','y'),
#              fun_names=c('Sum','Mean','Median'),
#              additional_code='Count=length(x)',
#              by=c('A'))
#    ##    Result:
#    #       A Sum__x Sum__y Mean__x Mean__y Median__x Median__y Count
#    #    1: a      6    306       2     102         2       102     3
#    #    2: b     15    315       5     105         5       105     3