Add (insert) a column between two columns in a data.frame

Question

I have a data frame that has columns a, b, and c. I\'d like to add a new column d between b and c.

I know I could just add d at the end by using cbind but h

Answer 1

R has no functionality to specify where a new column is added. E.g., mtcars$mycol<-'foo'. It always is added as last column. Using other means (e.g., dplyr's select()) you can move the mycol to a desired position. This is not ideal and R may want to try to change that in the future.

Answer 2

I would suggest you to use the function add_column() from the tibble package.

library(tibble)
dataset <- data.frame(a = 1:5, b = 2:6, c=3:7)
add_column(dataset, d = 4:8, .after = 2)

Note that you can use column names instead of column index :

add_column(dataset, d = 4:8, .after = "b")

Or use argument .before instead of .after if more convenient.

add_column(dataset, d = 4:8, .before = "c")

Answer 3

This function inserts one zero column between all pre-existent columns in a data frame.

insertaCols<-function(dad){   
  nueva<-as.data.frame(matrix(rep(0,nrow(daf)*ncol(daf)*2 ),ncol=ncol(daf)*2))  
   for(k in 1:ncol(daf)){   
      nueva[,(k*2)-1]=daf[,k]   
      colnames(nueva)[(k*2)-1]=colnames(daf)[k]  
      }  
   return(nueva)   
  }

Answer 4

You can use the append() function to insert items into vectors or lists (dataframes are lists). Simply:

df <- data.frame(a=c(1,2), b=c(3,4), c=c(5,6))

df <- as.data.frame(append(df, list(d=df$b+df$c), after=2))

Or, if you want to specify the position by name use which:

df <- as.data.frame(append(df, list(d=df$b+df$c), after=which(names(df)=="b")))

Answer 5

`

data1 <- data.frame(col1=1:4, col2=5:8, col3=9:12)
row.names(data1) <- c("row1","row2","row3","row4")
data1
data2 <- data.frame(col1=21:24, col2=25:28, col3=29:32)
row.names(data2) <- c("row1","row2","row3","row4")
data2
insertPosition = 2
leftBlock <- unlist(data1[,1:(insertPosition-1)])
insertBlock <- unlist(data2[,1:length(data2[1,])])
rightBlock <- unlist(data1[,insertPosition:length(data1[1,])])
newData <- matrix(c(leftBlock, insertBlock, rightBlock), nrow=length(data1[,1]), byrow=FALSE)
newData

`

Answer 6

When you can not assume that column b comes before c you can use match to find the column number of both, min to get the lower column number and seq_len to get a sequence until this column. Then you can use this index first as a positive subset, than place the new column d and then use the sequence again as a negative subset.

i <- seq_len(min(match(c("b", "c"), colnames(x))))
data.frame(x[i], d, x[-i])
#cbind(x[i], d, x[-i]) #Alternative
#  a b  d c
#1 1 4 10 7
#2 2 5 11 8
#3 3 6 12 9

In case you know that column b comes before c you can place the new column d after b:

i <- seq_len(match("b", colnames(x)))
data.frame(x[i], d, x[-i])
#  a b  d c
#1 1 4 10 7
#2 2 5 11 8
#3 3 6 12 9

Data:

x <- data.frame(a = 1:3, b = 4:6, c = 7:9)
d <- 10:12