Merging two types of columns in parallel using dplyr and tidyr

Question

I'm trying to port some code from plyr to dplyr .

In a specific case I got 2 kinds of columns I want to group together: nameX and propX (see sample data frame foo below), along with an id column. The result I got using ddply gives me a data frame with only 3 columns, id , name and prop (see data frame bar below).

library(plyr)

foo <- rbind(
  data.frame(
    id = 'A',
    name1 = "dXz",
    prop1 = 20,
    name2 = "Rpt",
    prop2 = 65,
    name3 = "YYq",
    prop3 = 15
  ),
  data.frame(
    id = 'B',
    name1 = "hut",
    prop1 = 30,
    name2 = "TPn",
    prop2 = 50,
    name3 = "pTm",
    prop3 = 20
  ),
  data.frame(
    id = 'C',
    name1 = "JpT",
    prop1 = 45,
    name2 = "Fil",
    prop2 = 25,
    name3 = "jjS",
    prop3 = 30
  )
)

bar <- ddply(
  foo, 
  .(id), 
  function(x) {
    data.frame(
      id = as.character(x$id), 
      name = c(as.character(x$name1), as.character(x$name2),as.character(x$name3),as.character(x$name4),as.character(x$name5)), 
      prop = c(x$prop1,x$prop2,x$prop3,x$prop4,x$prop5)
    )
  }
)

I have been trying to use the latest operators given by dplyr and tidyr , but I don't seem to be able to make two parallel groupings operations.

foo %>% 
  gather(name, prop, -id)

Answer 1

You're on the right track. The key is there are two things to consider here: First, you need to define which "name" and "prop" columns are supposed to go together. Second, you have to convert all the different column names to only two different names.

grps <- c("name1" = "g1",
         "prop1" = "g1",
         "name2" = "g2",
         "prop2" = "g2",
         "name1.1" = "g3",
         "prop2.1" = "g3")


foo %>% 
  tbl_df %>%
  gather(varname,value,-id) %>%
  mutate(grpname = grps[varname]) %>%
  mutate(varname2 = varname %>% grepl("^name",.) %>% ifelse("name",varname),
         varname3 = varname %>% grepl("^prop",.) %>% ifelse("prop",varname2)) %>%
  select(id,grpname,varname3,value) %>%
  spread(varname3,value)

  id grpname name prop
1  A      g1  dXz   20
2  A      g2  Rpt   65
3  A      g3  YYq   15
4  B      g1  hut   30
5  B      g2  TPn   50
6  B      g3  pTm   20
7  C      g1  JpT   45
8  C      g2  Fil   25
9  C      g3  jjS   30