Merge multiple variables in R

Question

I have a dataset such that the same variable is contained in difference columns for each subject. I want to merge them to the same columns.

E.g.:, I have this dataf

Answer 1

You can use coalesce from dplyr:

library(dplyr)

df %>%
  mutate(DV_1 = coalesce(DV1_A, DV1_B, DV1_C),
         DV_2 = coalesce(DV2_A, DV2_B, DV2_C))

If you have a lot of DV columns to combine, you might not want to type all the column names. In this case, you can first grep the column names for each DV, parse each name to symbols with rlang::syms, then splice (!!!) the symbols in coalesce (Advice from @hadley):

library(rlang)
var_quo1 = syms(grep("DV1", names(df), value = TRUE))
var_quo2 = syms(grep("DV2", names(df), value = TRUE))

df %>%
  mutate(DV_1 = coalesce(!!! var_quo1),
         DV_2 = coalesce(!!! var_quo2))

If instead, you have a ton of DV's, you might not even want to type all the coalesce lines, in this case, you can create a function that outputs one DV column given an input number and lapply + bind_col all of them together:

DV_combine = function(num_DVs){

  DV_name = sym(paste0("DV", num_DVs))
  DV_syms = syms(grep(paste0("DV", num_DVs), names(df), value = TRUE))

  df %>%
    transmute(!!DV_name := coalesce(!!! DV_syms))
}

bind_cols(df, lapply(1:2, DV_combine))

Result:

  ID DV1_A DV1_B DV1_C DV2_A DV2_B DV2_C FACT DV_1 DV_2
1  1     1    NA    NA     3    NA    NA    A    1    3
2  2    NA     4    NA    NA     3    NA    B    4    3
3  3    NA    NA     5    NA    NA     5    C    5    5

Note:

This method will work for both numeric and character class columns, but not factor's. One should first convert the factor columns to character before using this method.

Data:

df = structure(list(ID = c(1, 2, 3), DV1_A = c(1, NA, NA), DV1_B = c(NA, 
4, NA), DV1_C = c(NA, NA, 5), DV2_A = c(3, NA, NA), DV2_B = c(NA, 
3, NA), DV2_C = c(NA, NA, 5), FACT = structure(1:3, .Label = c("A", 
"B", "C"), class = "factor")), .Names = c("ID", "DV1_A", "DV1_B", 
"DV1_C", "DV2_A", "DV2_B", "DV2_C", "FACT"), row.names = c(NA, 
-3L), class = "data.frame")