Create new column using grouped column and numeric column from different data frame

I have two data frames (regionSum and areaSum) shown below.

Area	Region	void_pts
0	010	0.125
1	110	1.566
1	111	1.350
3	310	2.004
3	312	1.652

Area	void_pts
0	0.455
1	1.436
2	1.396
3	1.981

I'm trying to create a new column (alert) in the regionSum dataframe using these two conditions: regionSum$void_pts >= areaSum$void_pts and regionSum$area == areaSum$area.

Here is a snippet of the code that I've tried to use but its errors out.

t  %>% 
  mutate(alert = case_when(void_pts >= areaSum$void_pts & area == areaSum$area ~ "Red",
                                    TRUE ~ "Blue" )

What am I missing to give me the below results and how'd I go by tackling the same problem in the case of a lot of factors of the area field?

Area	Region	void_pts	alert
0	010	0.125	blue
1	110	1.566	red
1	111	1.350	blue
3	310	2.004	red
3	312	1.652	blue

CodePudding user response：

We can perform a join:

library(dplyr)

regionSum %>% inner_join(areaSum, by = c('Area' = 'Area')) %>% mutate(alert = case_when(void_pts.x >= void_pts.y ~ "Red",
                                                                                         TRUE ~ "Blue" ))
# A tibble: 5 × 5
   Area Region void_pts.x void_pts.y alert
  <dbl> <chr>       <dbl>      <dbl> <chr>
1     0 010         0.125      0.455 Blue 
2     1 110         1.57       1.44  Red  
3     1 111         1.35       1.44  Blue 
4     3 310         2.00       1.98  Red  
5     3 312         1.65       1.98  Blue

CodePudding user response：

Here is an option to achieve this:

regionSum  %>% 
  left_join(areaSum, by = "Area", suffix = c("_region", "_area")) %>%
  mutate(alert = case_when(void_pts_region >= void_pts_area ~ "Red", TRUE ~ "Blue" ))

  Area Region void_pts_region void_pts_area alert
1    0     10           0.125         0.455  Blue
2    1    110           1.566         1.436   Red
3    1    111           1.350         1.436  Blue
4    3    310           2.004         1.981   Red
5    3    312           1.652         1.981  Blue

Data

regionSum = structure(list(Area = c(0, 1, 1, 3, 3), Region = c(10, 110, 111, 
310, 312), void_pts = c(0.125, 1.566, 1.35, 2.004, 1.652)), class = "data.frame", row.names = c(NA, 
-5L))

areaSum = structure(list(Area = c(0, 1, 2, 3), void_pts = c(0.455, 1.436, 
1.396, 1.981)), class = "data.frame", row.names = c(NA, -4L))