Append text to a field based on another field's value - r

Question

I want to append a text based on another field's value. For example:-
This is the current df:
field_x <- c("A", "A", "C", "B", "B", "C")
field_y <- c("Axl", "Slash", "Duff", "Steven", "Izzy", "Dizzy")
df <- cbind(field_x, field_y)
I need to change the field_y based on field_x values so that it looks like this:
field_x <- c("A", "A", "C", "B", "B", "C")
field_y <- c("Axl (Apple)", "Slash (Apple)", "Duff (Cat)", "Steven (Ball)", "Izzy (Ball)", "Dizzy (Cat)")
So, basically if field_x has "A" then "(Apple)" is to be appended to field_y and so forth. Thanks in advance!

Answer 1

First note that your df is actually a matrix: when you cbind vectors, you get a matrix. So first thing to do is convert to dataframe.
Then it depends on whether or not you are using dplyr.
field_x <- c("A", "A", "C", "B", "B", "C")
field_y <- c("Axl", "Slash", "Duff", "Steven", "Izzy", "Dizzy")
df <- cbind(field_x, field_y)
df <- as.data.frame(df)
Without dplyr:
df <- within(df, {
s <- ifelse(field_x == "A", "Apple", ifelse(field_x == "B", "Ball", "Cat"))
field_y <- paste0(field_y, "(", s, ")")
rm(s)
})
With dplyr:
library(dplyr)
library(stringr)
library(magrittr)
df %<>%
mutate(
s = recode(field_x, "A" = "Apple", "B" = "Ball", "C" = "Cat"),
field_y = str_glue("{field_y}({s})")) %>%
select(-s)
Another way, with case_when instead of recode:
df %<>%
mutate(
s = case_when(
field_x == "A" ~ "Apple",
field_x == "B" ~ "Ball",
field_x == "C" ~ "Cat"
),
field_y = str_glue("{field_y}({s})")) %>%
select(-s)
Note that I create an auxiliary variable s: it's not really necessary, but it makes the code more readable.

Answer 2

Here is another approach:
We could create a look-up table to address the concerns of #Tim Biegeleisen in the comment section:
look_up <- data.frame(x = c("A", "B" ,"C"),
y = c("Apple", "Ball", "Cat"))
library(dplyr)
df %>%
as.data.frame() %>%
rowwise() %>%
mutate(field_y = paste0(field_y, ' (', look_up$y[look_up$x==field_x], ')'))
field_x field_y
<chr> <chr>
1 A Axl (Apple)
2 A Slash (Apple)
3 C Duff (Cat)
4 B Steven (Ball)
5 B Izzy (Ball)
6 C Dizzy (Cat)