R Add column to Table from two tables based on column value - r

Question

I have three tables that I'm attempting to merge into one.
The main table is similar to:
Table1 <- data.frame("Data" = c(1, 2, 3, 4, 5), "Desc" = c("A", "A", "A", "B", "B"))
TableA <- data.frame("Values" = c(6, 2, 3))
TableB <- data.frame("Values" = c(2, 7))
I want to add another column to Table1 with the values from TableA and TableB, but Values coming from TableA must be placed in a row containing "A" in the "Desc" column and TableB values in rows containing "B" in the "Desc" column. The number of rows in Table A equal the number of rows Table1 with "A" and same for TableB.
The resulting Table should look like:
Table1 <- data.frame("Data" = c(1, 2, 3, 4, 5), "Desc" = c("A", "A", "A", "B", "B"), "Values" = c(6, 2, 3, 2, 7))
> Table1
Data Desc Values
1 1 A 6
2 2 A 2
3 3 A 3
4 4 B 2
5 5 B 7

Answer 1

First note that these are "data.frames", not "tables". A "table" is actually a different class in R and they aren't the same thing. This strategy should work
Table1$Values <- NA
Table1$Values[Table1$Desc=="A"] <- TableA$Value
Table1$Values[Table1$Desc=="B"] <- TableB$Value
Table1
# Data Desc Values
# 1 1 A 6
# 2 2 A 2
# 3 3 A 3
# 4 4 B 2
# 5 5 B 7

Answer 2

If you have multiple Table (TableA, TableB, TableC,...etc) and if you need to match the suffix of Table. to Table1 column Desc
ls1 <- ls(pattern="Table")
ls1
#[1] "Table1" "TableA" "TableB"
library(stringr)
indx <- str_extract(ls1[-1], perl('(?<=Table)[A-Z]'))
lst1 <- mget(ls1[-1])
do.call(rbind,
lapply(seq_along(lst1),function(i) {
x1 <- lst1[[i]]
x2 <- Table1[!is.na(match(Table1$Desc, indx[i])),]
x2$Values <- x1$Values
x2}
))
# Data Desc Values
#1 1 A 6
#2 2 A 2
#3 3 A 3
#4 4 B 2
#5 5 B 7
In the first step, after I created the objects (Table.), looked for the object names ls(pattern="Table")
Extracted the suffix LETTERS A, B from the objects that needs to be matched. Used regex lookbehind i.e. (?<=Table)[A-Z] matches a substring (uppercase letter) preceded by the string Table and extract the substring.
mget returns the value of the objects as a list
Loop using lapply. Match the Desc column in Table1 with the extracted suffix and created a new column