基于列值的字符串连接

Question

How can I create a new column "desc" based on the value of column "num"?

Here is my original dataset. a, b, c, d, e, and f are rownames.

Here is the output I am looking for. Notice that "desc" consists of the rownames of column "num". The rownames of num 2 are b and d; hence desc of num 2 is "Var : b, d." The rownames of num 3 are c, e, f; hence desc of num 3 is "Var : c, e, f."

Here is the code to create the dataset.

df <- data.frame(num=c(1, 2, 3, 4, 3, 3))
rownames(df) <- c("a", "b", "c", "d", "e", "f")

Answer 1

We create a column from row names ( rownames_to_column ), grouped by 'num', create the 'desc' by paste ing the elements of the row names column ('rn')

library(tidyverse)
df %>% 
  rownames_to_column('rn') %>% 
  group_by(num) %>% 
  transmute(desc = paste0('var: ', toString(rn)))
# A tibble: 6 x 2
# Groups:   num [3]
#    num desc        
#  <dbl> <chr>       
#1     1 var: a      
#2     2 var: b, d   
#3     3 var: c, e, f
#4     2 var: b, d   
#5     3 var: c, e, f
#6     3 var: c, e, f

data

df <- structure(list(num = c(1, 2, 3, 2, 3, 3)), 
   class = "data.frame", row.names = c("a", 
  "b", "c", "d", "e", "f"))

Answer 2

transform(df, desc = ave(row.names(df), df$num, FUN = function(x) toString(x)))
#  num    desc
#a   1       a
#b   2       b
#c   3 c, e, f
#d   4       d
#e   3 c, e, f
#f   3 c, e, f