Return row(i) if two columns match - r

Question

I have two datasets:
df1
ID paddock cow ID
90/123 10 09/123
90/124 11 09/124
90/125 11 09/124
df2
ID paddock
09/123 20
09/124 21
I would like to match df1$cowID with df2$ID and return df2$paddock for whatever row matches. My current code is as follows:
dt <- ifelse(df1$cowID %in% df2$ID, df2$paddock[i], NA)
But I'm getting a return error. Could someone direct me in the right direction please? Thanks in advance!

Answer 1

You might consider joining the datasets.
dplyr::left_join(df1, df2, by = c('cow ID', 'ID')

Answer 2

You should probably use match :
df1$df2_paddock <- df2$paddock[match(df1$cow_ID, df2$ID)]
df1
# ID paddock cow_ID df2_paddock
#1 90/123 10 09/123 20
#2 90/124 11 09/124 21
data
df1 <- structure(list(ID = structure(1:2, .Label = c("90/123", "90/124"
), class = "factor"), paddock = 10:11, cow_ID = structure(1:2, .Label = c("09/123",
"09/124"), class = "factor")), class = "data.frame", row.names = c(NA, -2L))
df2 <- structure(list(ID = structure(1:2, .Label = c("09/123", "09/124"
), class = "factor"), paddock = 20:21), class = "data.frame",
row.names = c(NA, -2L))

Answer 3

You can do that by joining the two dataframes and getting the column that you want.
Using Base R
df1 <-
data.frame(
ID = c("90/123", "90/124"),
paddock = c(10, 11),
cow_ID = c("09/123", "09/124")
)
df2 <-
data.frame(
ID = c("90/123", "90/124"),
paddock = c(20, 21)
)
# Joining the two dataframes by ID then choosing coloum of interest
merge(df1, df2, by = c("ID"), suffixes = c(".x", ".y"))["paddock.y"]
# paddock.y
# 20
# 21
Using Dplyr
library(dplyr)
df1 <-
data.frame(
ID = c("90/123", "90/124"),
paddock = c(10, 11),
cow_ID = c("09/123", "09/124")
)
df2 <-
data.frame(
ID = c("90/123", "90/124"),
paddock = c(20, 21)
)
# Joining the two dataframes by ID then choosing coloum of interest
df1 %>%
inner_join(df2, by = c("ID"), suffixes = c(".x", ".y")) %>%
select(paddock.y) %>%
rename(paddock = paddock.y)
# paddock
# 20
# 21

Answer 4

If you would like to use ifelse(), maybe you can use the following code to make it
with(df2,ifelse(ID %in% df1$cow_ID,paddock,NA))
such that
> with(df2,ifelse(ID %in% df1$cow_ID,paddock,NA))
[1] 20 21
DATA
df1 <- structure(list(ID = structure(1:3, .Label = c("90/123", "90/124",
"90/125"), class = "factor"), paddock = c(10, 11, 11), cow_ID = structure(c(1L,
2L, 2L), .Label = c("09/123", "09/124"), class = "factor")), class = "data.frame", row.names = c(NA,
-3L))
df2 <- structure(list(ID = structure(1:2, .Label = c("09/123", "09/124"
), class = "factor"), paddock = c(20, 21)), class = "data.frame", row.names = c(NA,
-2L))