Comments, because this code does not document itself

12.R

 library(stringr)
 library(dplyr)
 
+# Make a dataframe of input, with column 2 as the letter and column 3 as the number
 input <- readLines("input12.txt") %>% str_match("^(\\w)(\\d+)$") %>% as.data.frame(stringsAsFactors = FALSE)
 names(input) <- c("Orig", "Arg", "Param")
 
 input %>% mutate(
-                 Param = as.numeric(Param),
-                 angChange = ifelse(Arg == "R", Param, ifelse(Arg == "L", -Param, 0)),
-                 Angle = cumsum(angChange) %% 360,
+                 Param = as.numeric(Param), # Make number numeric type
+                 angChange = ifelse(Arg == "R", Param, ifelse(Arg == "L", -Param, 0)), # Calculate what each R/L does to the angle
+                 Angle = cumsum(angChange) %% 360, # Calculate running angle, within 0-359
+                 # Calculate amount to move East, South at each line
                  MovEast = ifelse(Arg == "E", Param,
                                   ifelse(Arg == "W", -Param,
                                          ifelse(Arg == "F", cos(Angle * pi / 180) * Param, 0))),
                  MovSouth = ifelse(Arg == "S", Param,
                                   ifelse(Arg == "N", -Param,
                                          ifelse(Arg == "F", sin(Angle * pi / 180) * Param, 0))),
+                 # Running tally of position
                  PosEast = cumsum(MovEast),
                  PosSouth = cumsum(MovSouth)
                  ) -> shipsLog
 
+# Calculate manhattin distance
 mandist <- abs(sum(shipsLog$MovEast)) + abs(sum(shipsLog$MovSouth))
 
+# Drop stuff from previous dataframe that wont be used this time
 shipsLog %>% select(Orig:Angle) %>%
     mutate(
+           # Calculate the east, south amount being specified by param value
            tPMovEast = ifelse(Arg == "E", Param, ifelse(Arg == "W", -Param, 0)),
            tPMovSouth = ifelse(Arg == "S", Param, ifelse(Arg == "N", -Param, 0)),
+           # Convert to a rotating reference frame according to the angle
            PMovEast = ifelse(Angle == 0, tPMovEast,
                              ifelse(Angle == 90, tPMovSouth,
                                     ifelse(Angle == 180, -tPMovEast,
                               ifelse(Angle == 90, -tPMovEast,
                                      ifelse(Angle == 180, -tPMovSouth,
                                             tPMovEast))),
+           # Calculate running position of waypoint in rotated frame
            PREastPos = cumsum(PMovEast) + 10,
            PRSouthPos = cumsum(PMovSouth) - 1,
+           # Return to original fixed reference frame
            PTEastPos = ifelse(Angle == 0, PREastPos,
                               ifelse(Angle == 90, -PRSouthPos,
                                      ifelse(Angle == 180, -PREastPos,
                               ifelse(Angle == 90, PREastPos,
                                      ifelse(Angle == 180, -PRSouthPos,
                                             -PREastPos))),
+           # Calculate movement of ship at each line
            ShipMoveEast = ifelse(Arg == "F", Param * PTEastPos, 0),
            ShipMoveSouth = ifelse(Arg == "F", Param * PTSouthPos, 0)
            ) -> shipsLog2
                                            
 
+# Calculate manhattin distance
 mandist2 <- abs(sum(shipsLog2$ShipMoveEast)) + abs(sum(shipsLog2$ShipMoveSouth))