Gather multiple date/value columns using tidyr

Question

I have a data set containing (amongst others) multiple columns with dates and corresponding values (repeated measurements). Is there a way to turn this into a long data set

Answer 1

I stumbled across this trying to learn about using gather with a mix of dates and values.

The existing answers lose information about which instance the date-value pair came from, ie, instance 1 for date1 & value1, etc. This may not be important, but here's a tidyverse option that keeps the instance.

library(stringr) # not necessary but nice
library(tidyr)
library(dplyr)

df %>% 
    gather(key, val, -id, -age) %>% 
    mutate(
        measure = str_sub(key,1,-2), 
        instance = str_sub(key, -1)
    ) %>% 
    select(-key) %>% 
    spread(measure, val) %>% 
    mutate(date = as.Date(date, origin="1970-01-01")) # restore date class