How to make smaller table grow and match the contents of larger table in R? - sql

Question

I have three columns. The first is large and contains various letters. The second is the same size but contains fewer letters with some NAs. Each letter can be found in the larger column. The third is the same size also but contains values with the second column and corresponding NAs.
My question is how do I make it so that the second and third column are re-arranged so that the second column matches the first column where possible.
I feel the answer is something to do with left join but I can't figure it out.
A bit weird to explain in words but example shows it easily.
# Original Situation
Large <- c("B", "D", "C", "A", "E")
Small <- c("D", "A", NA, NA, NA)
Number <- c(5, 12, NA, NA, NA)
data.frame(Large, Small, Number)
#> Large Small Number
#> 1 B D 5
#> 2 D A 12
#> 3 C <NA> NA
#> 4 A <NA> NA
#> 5 E <NA> NA
# I want it to finish like this:
Large <- c("B", "D", "C", "A", "E")
Small <- c(NA, "D", NA, "A", NA)
Number <- c(NA, 5, NA, 12, NA)
data.frame(Large, Small, Number)
#> Large Small Number
#> 1 B <NA> NA
#> 2 D D 5
#> 3 C <NA> NA
#> 4 A A 12
#> 5 E <NA> NA

Answer 1

library(dplyr)
# I find `tibble` generally better than `data.frame`
# If you want to use `data.frame` remember to especify stringAsFactors = FALSE
df_large <- tibble(large = Large)
df_small <- tibble(small = Small, number = Number)
left_join(df_large, df_small, by = c("large" = "small"))
If you want to keep both large and small columns (I don't really see a reason to):
left_join(df_large, df_small, by = c("large" = "small")) %>%
mutate(small = if_else(!is.na(number), large, NA_character_))
# A tibble: 5 x 3
large number small
<chr> <dbl> <chr>
1 B NA NA
2 D 5 D
3 C NA NA
4 A 12 A
5 E NA NA

Answer 2

Here is a base way:
x <- df[1]
y <- setNames(df[c(2, 2, 3)], names(df))
merge(x, y, all.x = T)
# Large Small Number
# 1 A A 12
# 2 B <NA> NA
# 3 C <NA> NA
# 4 D D 5
# 5 E <NA> NA
Use the same logic on left_join():
library(tidyverse)
df %>%
mutate(Large = Small) %>%
right_join(df[1])
# Large Small Number
# 1 B <NA> NA
# 2 D D 5
# 3 C <NA> NA
# 4 A A 12
# 5 E <NA> NA