syntax for nested ifelse and if statements in R-CodePudding

I am trying to nest if and/or ifelse statements together in R and I can't quite get the syntax correct. I would like to perform some basic arithmetic: Referencing a similar dataset below, if the date is the same and if the location code is the same, I would like to subtract the pH values of codes A and B from the corresponding pH value for code F and enter the result into pHDelta. Or written out, A - F for a given date and location.

Thank you!

I am not certain the daset that I created below will appear correctly, please pardon me if it does not.

My dataset is similar to the following:

Date	Location	Code	pH
22/07/01	AA	A	7.1
22/07/01	AA	B	6.8
22/07/01	AA	F	8.2
22/07/01	AB	A	7. 2
22/07/01	AB	B	7.8
22/07/01	AB	F	8.4
22/07/01	AC	A	7.5
22/07/01	AC	B	6.2
22/07/01	AC	F	8.3
22/07/01	AD	A	7.1
22/07/01	AD	B	6.8
22/07/01	AD	F	8.2
22/07/02	AA	A	7.1
22/07/02	AA	B	6.8
22/07/02	AA	F	8.2
22/07/02	AB	A	7.2
22/07/02	AB	B	7.8
22/07/02	AB	F	8.4
22/07/02	AC	A	7.5
22/07/02	AC	B	6.2
22/07/02	AC	F	8.3
22/07/02	AD	A	7.1
22/07/02	AD	B	6.8
22/07/02	AD	F	8.2

CodePudding user response：

We can use a group by approach - grouped by 'Date', 'Location', subset the 'pH' where 'Code' value is "F" (assuming only a single "F" per Location) and then subtract from the 'pH' column

library(dplyr)
df1 <- df1 %>%
     group_by(Date, Location) %>%
     mutate(phDelta = pH - pH[Code == "F"]) %>%
     ungroup

CodePudding user response：

Another approach: Because of the repetitive calculations we could also do:

library(dplyr)

df %>% 
  group_by(Date, Location) %>% 
  arrange(Code, .by_group = TRUE) %>% 
  mutate(pHDelta = pH-last(pH)) %>% 
  ungroup()

  Date     Location Code     pH pHDelta
   <chr>    <chr>    <chr> <dbl>   <dbl>
 1 22/07/01 AA       A       7.1  -1.1  
 2 22/07/01 AA       B       6.8  -1.4  
 3 22/07/01 AA       F       8.2   0    
 4 22/07/01 AB       A       7.2  -1.2  
 5 22/07/01 AB       B       7.8  -0.600
 6 22/07/01 AB       F       8.4   0    
 7 22/07/01 AC       A       7.5  -0.800
 8 22/07/01 AC       B       6.2  -2.1  
 9 22/07/01 AC       F       8.3   0    
10 22/07/01 AD       A       7.1  -1.1  
# ... with 14 more rows

data:

structure(list(Date = c("22/07/01", "22/07/01", "22/07/01", "22/07/01", 
"22/07/01", "22/07/01", "22/07/01", "22/07/01", "22/07/01", "22/07/01", 
"22/07/01", "22/07/01", "22/07/02", "22/07/02", "22/07/02", "22/07/02", 
"22/07/02", "22/07/02", "22/07/02", "22/07/02", "22/07/02", "22/07/02", 
"22/07/02", "22/07/02"), Location = c("AA", "AA", "AA", "AB", 
"AB", "AB", "AC", "AC", "AC", "AD", "AD", "AD", "AA", "AA", "AA", 
"AB", "AB", "AB", "AC", "AC", "AC", "AD", "AD", "AD"), Code = c("A", 
"B", "F", "A", "B", "F", "A", "B", "F", "A", "B", "F", "A", "B", 
"F", "A", "B", "F", "A", "B", "F", "A", "B", "F"), pH = c(7.1, 
6.8, 8.2, 7.2, 7.8, 8.4, 7.5, 6.2, 8.3, 7.1, 6.8, 8.2, 7.1, 6.8, 
8.2, 7.2, 7.8, 8.4, 7.5, 6.2, 8.3, 7.1, 6.8, 8.2)), class = "data.frame", row.names = c(NA, 
-24L))