map values

library(data.table)
library(plyr)
library(dplyr)
library(tidyr)
library(magrittr)

# data generation
set.seed(100)
dt = data.table(t(replicate(100, sample(letters, 5)))) %>%
  setnames(paste0("id", 1:5))
mapTable = data.table(value = letters, score = sample(1:100, 26))

# solution
dt %>% mutate(rowNum = 1:nrow(.)) %>% gather(id, value, -rowNum) %>%
  mutate(score = mapvalues(value, mapTable$value, mapTable$score)) %>%
  group_by(rowNum) %>% summarise(med_score = median(score))