Useful R snippets

A collection of useful R snippets

library(tidyverse)

Create a new column with a value from a specific cell

Take the following simple data frame:

df <- tribble(
  ~x, ~y,
  "A", 0.1,
  "B", 0.4,
  "C", 0.2,
  "D", 0.3,
  "E", 0.5
)

df

x	y
A	0.1
B	0.4
C	0.2
D	0.3
E	0.5

Using the following code, we can add a new column that repeats a specific value from column y based on a value in a column x.

df <- mutate(df, z = nth(y, which(x == "B")))
df

x	y	z
A	0.1	0.4
B	0.4	0.4
C	0.2	0.4
D	0.3	0.4
E	0.5	0.4

This can be useful if you want to do scaling based on specific values.

df |>
  mutate(y_scaled = y / z)

x	y	z	y_scaled
A	0.1	0.4	0.25
B	0.4	0.4	1.00
C	0.2	0.4	0.50
D	0.3	0.4	0.75
E	0.5	0.4	1.25