Match row value with column name and extract value in R

Question

I have a table where I need to choose all the values in the Data column, match with the column names and take the value from that row. Ex. Data column: choose A1, find colu

Answer 1

What about this?

df[cbind(1:4, match(df$Data, names(df)))]
[1] "1"  "6"  "11" NA

Answer 2

If you create your data.frame with the row.names as your Data column, then it can be as simple as:

mydf <- read.table(text = "A1 A2 A3 Data 
1 5 9 A1
2 6 10 A2 
3 7 11 A3 
4 8 12 A4", header = TRUE, row.names = "Data")

sapply(row.names(mydf), function(x) mydf[[x, x]])
## $A1
## [1] 1
## 
## $A2
## [1] 6
## 
## $A3
## [1] 11
## 
## $A4
## NULL
## 

mydf[x,x] simply returns the element of my df, in the row with the name x and the column with name x. You may need to tweak this output to match your goal.