CODEWITHSUNDEEP
rdplyr
Paul Lemmens
Paul Lemmens

Reputation: 625

Reverse ordering dplyr's group_ by()

I'm writing a print method for a package that I'm working on. It's basic task is to display a set of tasks grouped by date. Because working on a console implies that the last thing printed is closest to the prompt, I want the oldest date to be listed last. Without all the hassle of the print method and dispatching, the core code is something along this:

d <- data.frame(thr = as.Date(Sys.time()) + seq(-3,3,1),
                tsk = paste0('t', 1:7), stringsAsFactors = FALSE)
d %>% group_by(thr) %>% 
  do(x = {
      thr <- format(.$thr, '%d-%m-%Y')
      cat(thr, '\n', .$tsk, '\n') 
     })

This generates

02-09-2015 
 t1 
03-09-2015 
 t2 
04-09-2015 
 t3 
05-09-2015 
 t4 
06-09-2015 
 t5 
07-09-2015 
 t6 
08-09-2015 
 t7

But I'd like to order it in reverse chronological order so that the oldest date is printed last:

08-09-2015
 t7
07-09-2015
 t6 
...

In normal (non printing code) this would be easy using arrange(-thr) but I haven't figured out a way to do this in the print function.

Upvotes: 1

Views: 2190

Answers (2)

bramtayl
bramtayl

Reputation: 4024

Answer with NA's moved to the top.

library(dplyr)
library(magrittr)
options(stringsAsFactors = FALSE)

data.frame(thr = 
             as.Date(Sys.time()) + c(seq(-3,3,1), seq(-3,3,1)) %>%
             c(NA),
           tsk = paste0('t', 1:15)) %>%
  arrange(tsk) %>%
  group_by(thr) %>%
  summarize(
    tsk_out = 
      paste(
        thr %>% first %>% format('%d-%m-%Y'),
        '\n',
        tsk %>% unique %>% paste(collapse = " "),
        '\n') ) %>%
  arrange(thr %>% order(na.last = FALSE, decreasing = TRUE)) %>% 
  use_series(tsk_out) %>%
  cat

Upvotes: 1

bramtayl
bramtayl

Reputation: 4024

library(dplyr)
library(magrittr)

data.frame(thr = as.Date(Sys.time()) + c(seq(-3,3,1), seq(-3,3,1)),
           tsk = paste0('t', c(1:14)), stringsAsFactors = FALSE) %>%
  arrange(tsk) %>%
  group_by(thr) %>%
  summarize(
    tsk_out = 
      paste(
        thr %>% first %>% format('%d-%m-%Y'),
        '\n',
        tsk %>% unique %>% paste(collapse = " "),
        '\n') ) %>%
  arrange(desc(thr)) %>%
  use_series(tsk_out) %>%
  cat

Upvotes: 3

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