Set column value using the first next row in the same group that meets a condition

Question

I am new to R and this is my first question on stackoverflow.

I am trying

• to assign by reference to a new column
• for each row
• using the v

Answer 1

A Not-the-Data-Table-Way approach:

> df <- structure(list(
+   id        = c(1L, 1L, 2L, 2L, 3L, 4L, 5L, 5L, 5L, 6L, 6L, 6L),
+   code      = c("p", "f", "f", "p", "p", "", "f", "p", "p", "f", "p", "p"),
+   date_down = structure(c(17897, 17898, 17898, 17899, 17900, 17901, 17903, 17903, 17905, 17906, 17906, 17906), class = "Date"),
+   date_up   = structure(c(17898, 17899, 17898, NA, NA, 17901, 17904, 17904, 17905, 17906, 17906, 17907), class = "Date")),
+   class     = c("data.frame"),
+   row.names = c(NA, -12L))
> 
> 
> Lista <- lapply(split(df, df$id), function(x){
+   x$founddate <- 
+     sapply(c(1:nrow(x)), function(y){
+       na.omit(sapply(y:nrow(x), function(i){
+         ifelse(x[i + 1, "code"] == "p" & x[i + 1, "date_up"] > x[y, "date_down"],
+                x[i + 1, "date_up"], NA)
+       }))[1]
+     })
+   x$founddate <- as.Date(x$founddate, origin = "1970-01-01")
+   return(x)
+ })
> 
> 
> df <- do.call(rbind.data.frame, Lista)
> 
> df
     id code  date_down    date_up  founddate
1.1   1    p 2019-01-01 2019-01-02       
1.2   1    f 2019-01-02 2019-01-03       
2.3   2    f 2019-01-02 2019-01-02       
2.4   2    p 2019-01-03              
3     3    p 2019-01-04              
4     4  2019-01-05 2019-01-05       
5.7   5    f 2019-01-07 2019-01-08 2019-01-08
5.8   5    p 2019-01-07 2019-01-08 2019-01-09
5.9   5    p 2019-01-09 2019-01-09       
6.10  6    f 2019-01-10 2019-01-10 2019-01-11
6.11  6    p 2019-01-10 2019-01-10 2019-01-11
6.12  6    p 2019-01-10 2019-01-11       
> 

Under the given conditions, there are more than one match per row. The proposed answer gets the first match, but this can be modified.

Hope it helps.