How to combine unknown number of data frames in R? - r

Question

Data
I have a data frame df. Following is a sample:
df <- data.frame(ID = rep(c(-1,7,8), each=3), LV.vel.fps = 40:48, frames = 1:9)
And there are unknown number of other data frames, each with the prefix "comb." followed by a number. Each of these data frames represent data for a vehicle. Following data frame contains names of those vehicles (These numbers change based on the experiment so, there are 2 vehicles now but after another experiment there could be 9):
> ADO.names
name
1 TrucPropk
2 Truck
So, nrow(ADO.names) tells us how many data frames there are. Following are the "comb." data frames for this particular example:
comb.1 <- data.frame(frames = 4:6, ADO.name = "TrucPropk", speed.fps = 43:45)
comb.2 <- data.frame(frames = 7:9, ADO.name = "Truck", speed.fps = 46:48)
Also, these data frames could have different number of rows.
What I want to do
The "ID" variable in df contains the IDs of the vehicles in the "comb." data frames. -1 means no vehicle. The IDs are not available in the "comb." data frames but I want to add a new column "final.name" in df that contains the name of the vehicle for a given ID. This can be done by matching "speed.fps" from "comb." to "LV.vel.fps" in df because both are speeds in feet per second.
Therefore, the final output should look like this:
> df
ID LV.vel.fps frames final.name
1 -1 40 1 NA
2 -1 41 2 NA
3 -1 42 3 NA
4 7 43 4 TrucPropk
5 7 44 5 TrucPropk
6 7 45 6 TrucPropk
7 8 46 7 Truck
8 8 47 8 Truck
9 8 48 9 Truck
Problems
For these sample data frames, I could do following for joining data frames:
library(dplyr)
df <- df %>%
left_join(x = ., y = comb.1, by = "frames") %>%
left_join(x = ., y = comb.2, by = "frames")
And ifelse for "final.name":
df$final.name <- ifelse(df$speed.fps.x==df$LV.vel.fps,
df$ADO.name.x,
ifelse(df$speed.fps.y==df$LV.vel.fps,
df$ADO.name.y, "NA"))
But the output I get is wrong:
> df
ID LV.vel.fps frames final.name ADO.name.x speed.fps.x ADO.name.y speed.fps.y
1 -1 40 1 NA <NA> NA <NA> NA
2 -1 41 2 NA <NA> NA <NA> NA
3 -1 42 3 NA <NA> NA <NA> NA
4 7 43 4 1 TrucPropk 43 <NA> NA
5 7 44 5 1 TrucPropk 44 <NA> NA
6 7 45 6 1 TrucPropk 45 <NA> NA
7 8 46 7 NA <NA> NA Truck 46
8 8 47 8 NA <NA> NA Truck 47
9 8 48 9 NA <NA> NA Truck 48
Questions
So basically I have 2 questions:
1) How do I write code so that all "comb." data frames are joined with df regardless of number of those data frames? I knew there were 2 in this case so manually wrote "comb.1" and "comb.2" But the code should be robust for any number of data frames.
2) Why is my ifelse statement not generating correct output? How could I write robust code for this case as well?

Answer 1

We can get the data.frame object names that starts with comb in a list using mget, rbind the list elements and then merge with the dataset 'df'.
res <- merge(df, do.call(rbind,
mget(ls(pattern='^comb\\.\\d+')))[1:2], by='frames', all.x=TRUE)
colnames(res)[4] <- 'final.name'
res
# frames ID LV.vel.fps final.name
#1 1 -1 40 <NA>
#2 2 -1 41 <NA>
#3 3 -1 42 <NA>
#4 4 7 43 TrucPropk
#5 5 7 44 TrucPropk
#6 6 7 45 TrucPropk
#7 7 8 46 Truck
#8 8 8 47 Truck
#9 9 8 48 Truck
EDIT: As the OP mentioned about matching the 'speed' columns, we can include that also in the merge
res <- merge(df,
do.call(rbind,mget(ls(pattern='^comb\\.\\d+'))),
by.x=c('frames', 'LV.vel.fps'), by.y= c('frames', 'speed.fps'),
all.x=TRUE)
colnames(res)[4] <- 'final.name'