Interesting tidy eval use cases

tidyverse
5

I can't claim credit, but I did ask the question that led @danr to provide this useful function (which Kieran Healey wrote about here) . It's essentially spread() but with multiple value arguments. I use it all the time, though I usually call it spread_n in my code.

df <- data.frame(month=rep(1:3,2),
                                 student=rep(c("Amy", "Bob"), each=3),
                                 A=c(9, 7, 6, 8, 6, 9),
                                 B=c(6, 7, 8, 5, 6, 7))

t1 <- df %>%
    gather(variable, value, -(month:student)) %>%
    unite(temp, student, variable) %>%
    spread(temp, value)
#   month Amy_A Amy_B Bob_A Bob_B
# 1     1     9     6     8     5
# 2     2     7     7     6     6
# 3     3     6     8     9     7

myspread <- function(df, key, value) {
    # quote key
    keyq <- rlang::enquo(key)
    # break value vector into quotes
    valueq <- rlang::enquo(value)
    s <- rlang::quos(!!valueq)
    df %>% gather(variable, value, !!!s) %>%
        unite(temp, !!keyq, variable) %>%
        spread(temp, value)
}

t2 <- df %>% myspread(student, c(A, B))

identical(t1, t2)
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