Combine multiple variables into new variable / Split Variable into 3 variables - r

Question

I need to create a 'key' variable, since I want to combine two datasets.
Dataset1 has the variable ymd.
Dataset2 has the three variables y, m and d.
ymd (20050516,20060512)
y(2005,2006)
m(05,05)
d(16,12)
Two Options:
Combine y,m and d into variable ymd
List item plit variable ymd into 3 variables y, m and d.

Answer 1

Assuming you have two data frames:
df1 <- data.frame(
ymd = c(20050516,20060512),
x = c(1,2)
)
df2 <- data.frame(
y = c(2005,2006),
m = c('05','05'),
d = c(16,12),
z = c(5,10)
)
You can merge by pasting together the y, m, and d elements using paste0 and changing to numeric:
df2 %>%
mutate(
ymd = as.numeric(paste0(y,m,d))
) %>%
left_join(df1)
Output:
>
Joining, by = "ymd"
y m d z ymd x
1 2005 05 16 5 20050516 1
2 2006 05 12 10 20060512 2
You can adjust the merge (eg right_join) depending on your needs.

Answer 2

Here you have an example.
I use the variables as string instead of numeric, which makes it easier. You can use as.character() as in my example to convert it.
For option 1, I just use paste0() to paste the text together.
For option 2 I use substr() to cut the text in the corect locations.
If you need the output as numeric and not string, just use as.numeric() as I did in the print function.
Here is the code, let me know if you have further question:
ymd=as.character(c(20050516,20060512))
y=as.character(c(2005,2006))
m=as.character(c(05,05))
d=as.character(c(16,12))
## Concatenade y, m, and d together
ymd_concatenated=paste0(y,m,d)
print(as.numeric(ymd_concatenated))
## Split ymd into single variables
y_concatenated=c()
m_concatenated=c()
d_concatenated=c()
for (date in ymd)
{
y_concatenated=c(y_concatenated,substr(date,1,4))
m_concatenated=c(m_concatenated,substr(date,5,6))
d_concatenated=c(d_concatenated,substr(date,7,8))
}
print(y_concatenated)
print(m_concatenated)
print(d_concatenated)