R frequency and element index, ranking

Question

I looked at this sample code below,

r element frequency and column name

and wondered if there was a way to show the index of each element in each column in addition to rank and frequency in r. therefore, for example, the desired input and output will be

df <- read.table(header=T, text='A    B    C    D
a    a    b    c
b    c    x    e
c    d    y    a
d   NA    NA     z
e  NA NA NA
f NA NA NA',stringsAsFactors=F) 

and conclusion

   element frequency columns ranking   A   B   C   D
1        a         3   A,B,D       1   1   1   na  2
3        c         3   A,B,D       1   3   2   na  1
2        b         2     A,C       2   2   na  1   na
4        d         2     A,B       2   4   3   na  na
5        e         2     A,D       2   5   na  na  2
6        f         1       A       3   6   na  na  na
8        x         1       C       3   na  na  2   na
9        y         1       C       3   na  na  3   na
10       z         1       D       3   na  na  na  3

Thank.

Answer 1

There may be a way to do this in one step, but it does not occur to me at the moment. So, continuing my previous answer :

library(dplyr)
library(tidyr)

step1 <- df %>%
  gather(var, val, everything()) %>%             ## Make a long dataset
  na.omit %>%                                    ## We don't need the NA values
  group_by(val) %>%                              ## All calculations grouped by val
  summarise(column = toString(var),              ## This collapses
            freq = n()) %>%                      ## This counts
  mutate(ranking = dense_rank(desc(freq)))       ## This ranks 

step2 <- df %>%
  mutate(ind = 1:nrow(df)) %>%                   ## Add an indicator column
  gather(var, val, -ind) %>%                     ## Go long
  na.omit %>%                                    ## Remove NA
  spread(var, ind)                               ## Go wide

inner_join(step1, step2)
# Joining by: "val"
# Source: local data frame [9 x 8]
# 
#   val  column freq ranking  A  B  C  D
# 1   a A, B, D    3       1  1  1 NA  3
# 2   b    A, C    2       2  2 NA  1 NA
# 3   c A, B, D    3       1  3  2 NA  1
# 4   d    A, B    2       2  4  3 NA NA
# 5   e    A, D    2       2  5 NA NA  2
# 6   f       A    1       3  6 NA NA NA
# 7   x       C    1       3 NA NA  2 NA
# 8   y       C    1       3 NA NA  3 NA
# 9   z       D    1       3 NA NA NA  4