Identifying values from one database to use in another database - r

Question

I am working on a project in which I need to work with 2 databases, identify values from one database to use in another.
I have a dataframe 1,
df1<-data.frame("ID"=c(1,2,3),"Condition A"=c("B","B","A"),"Condition B"=c("1","1","2"),"Year"=c(2002,1988,1995))
and a dataframe 2,
df2 <- data.frame("Condition A"=c("A","A","B","B"),"Condiction B"=c("1","2","1","2"),"<1990"=c(20,30,50,80),"1990-2000"=c(100,90,80,30),">2000"=c(300,200,800,400))
I would like to add a new column to df1 called "Value", in which, for each ID (from df1), collects the values from column 3,4 or 5 from df2 (depending on the year), and following conditions A and B available in both databases. The end result would be something like this:
df1<-data.frame("ID"=c(1,2,3),"Condition A"=c("B","B","A"),"Condition B"=c("1","1","2"),"Year"=c(2002,1988,1995),"Value"=c(800,50,90))
thanks!

Answer 1

I think we can simply left_join, then mutate with case_when, then drop the undesired columns with select:
library(dplyr)
left_join(df1, df2, by=c("Condition.A", "Condition.B"))%>%
mutate(Value=case_when(Year<1990 ~ X.1990,
Year<2000 ~ X1990.2000,
Year>=2000 ~ X.2000))%>%
select(-starts_with("X"))
ID Condition.A Condition.B Year Value
1 1 B 1 2002 800
2 2 B 1 1988 50
3 3 A 2 1995 90
EDIT: I edited your code, removing the "Condiction" typo

Answer 2

You could use
library(dplyr)
library(tidyr)
df2 %>%
rename(Condition.B = Condiction.B) %>%
pivot_longer(matches("\\d+{4}")) %>%
right_join(df1, by = c("Condition.A", "Condition.B")) %>%
filter(name == case_when(
Year < 1990 ~ "X.1990",
Year > 2000 ~ "X.2000",
TRUE ~ "X1990.2000")) %>%
select(ID, Condition.A, Condition.B, Year, Value = value) %>%
arrange(ID)
This returns
# A tibble: 3 x 5
ID Condition.A Condition.B Year Value
<dbl> <chr> <chr> <dbl> <dbl>
1 1 B 1 2002 800
2 2 B 1 1988 50
3 3 A 2 1995 90
At first we rename the misspelled column Condiction.B of df2 and bring it into a "long format" based on the "<1990", "1990-2000", ">2000" columns. Note that those columns can't be named like this, they are automatically renamed to X.1990, X1990.2000 and X.2000.
Next we use a right join with df1 on the two Condition columns.
Finally we filter just the matching years based on a hard coded case_when function and do some clean up (selecting and arranging).

Answer 3

We could do it this way:
Condiction must be a typo so I changed it to Condition
in df1 create a helper column that assigns each your to the group which is a column name in df2
bring df2 in long format
finally apply left_join by by=c("Condition.A", "Condition.B", "helper"="name")
library(dplyr)
library(tidyr)
df1 <- df1 %>%
mutate(helper = case_when(Year >=1990 & Year <=2000 ~"X1990.2000",
Year <1990 ~ "X.1990",
Year >2000 ~ "X.2000"))
df2 <- df2 %>%
pivot_longer(
cols=starts_with("X")
)
df3 <- left_join(df1, df2, by=c("Condition.A", "Condition.B", "helper"="name")) %>%
select(-helper)
ID Condition.A Condition.B Year value
1 1 B 1 2002 800
2 2 B 1 1988 50
3 3 A 2 1995 90