将占位符行添加到数据框列表

Question

I have a list of dataframes.

# Split dataframe into list of dataframes on two factor variables.
DF_list <- split(DF, list(DF$Unit_number, DF$Compartment), drop = TRUE)

I know how to remove rows from lists of dataframes. But this time I want to add rows. 1 placeholder row on the bottom of every dataframe in the list.

This will prevent my rate of change calculations from creating false calculations for different factor levels that buttress each other in the normal dataframe structure.

Before splitting on compartment and unit number the dataframe looks like this;

DF <- data.frame(Unit_number=c(1,1,2,2,2,1,2,2,1,1),
                 Compartment=c("Engine", "Engine", "Engine", "Transmission", "Transmission", "Transmission", "Tyres", "Tyres", "Tyres", "Tyres"))

The result needed is this;

Result <- data.frame(Unit_number=c(1,1,"Placeholder",2,"Placeholder",2,2,"Placeholder",1,"Placeholder",2,2,"Placeholder",1,1),
                 Compartment=c("Engine", "Engine","Placeholder", "Engine","Placeholder", "Transmission", "Transmission","Placeholder", "Transmission","Placeholder", "Tyres", "Tyres","Placeholder", "Tyres", "Tyres"))

Answer 1

If it's the same place holder that we want to add at the bottom of every list, we can create a Placeholder_df and rbind it at the end of every list.

Using purrr , map_dfr we could do

Placeholder_df <-data.frame(Unit_number = "Placeholder",
                            Compartment = "Placeholder")

purrr::map_dfr(DF_list, ~ rbind(., Placeholder_df))

#   Unit_number  Compartment
#1            1       Engine
#2            1       Engine
#3  Placeholder  Placeholder
#4            2       Engine
#5  Placeholder  Placeholder
#6            1 Transmission
#7  Placeholder  Placeholder
#8            2 Transmission
#9            2 Transmission
#10 Placeholder  Placeholder
#11           1        Tyres
#12           1        Tyres
#13 Placeholder  Placeholder
#14           2        Tyres
#15           2        Tyres
#16 Placeholder  Placeholder

---

In base R, we could do

do.call(rbind, lapply(DF_list, function(x) rbind(x, Placeholder_df)))

Answer 2

With base R , we can make use of Map

do.call(rbind, Map(rbind, DF_list, list(Placeholder_df)))

data

Placeholder_df <-data.frame(Unit_number = "Placeholder",
                        Compartment = "Placeholder")