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

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 how can I insert it in between two columns?

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")

Add in your new column:

df$d <- list/data

Then you can reorder them.

df <- df[, c("a", "b", "d", "c")]

You can reorder the columns with [, or present the columns in the order that you want.

d <- data.frame(a=1:4, b=5:8, c=9:12)
target <- which(names(d) == 'b')[1]
cbind(d[,1:target,drop=F], data.frame(d=12:15), d[,(target+1):length(d),drop=F])

  a b  d  c
1 1 5 12  9
2 2 6 13 10
3 3 7 14 11
4 4 8 15 12

Presuming that c always immediately follows b, this code will add a column after b no matter where b is in your data.frame.

> test <- data.frame(a=1,b=1,c=1)
> test
  a b c
1 1 1 1

> bspot <- which(names(test)=="b")

> data.frame(test[1:bspot],d=2,test[(bspot+1):ncol(test)])
  a b d c
1 1 1 2 1

Or possibly more naturally:

data.frame(append(test, list(d=2), after=match("b", names(test))))

Create an example data.frame and add a column to it.

df = data.frame(a = seq(1, 3), b = seq(4,6), c = seq(7,9))
df['d'] <- seq(10,12)
df

  a b c  d
1 1 4 7 10
2 2 5 8 11
3 3 6 9 12

Rearrange by column index

df[, colnames(df)[c(1:2,4,3)]]

or by column name

df[, c('a', 'b', 'd', 'c')]

The result is

  a b  d c
1 1 4 10 7
2 2 5 11 8
3 3 6 12 9

You would like to add column z to the old data frame (old.df) defined by columns x and y.

z = rbinom(1000, 5, 0.25)
old.df <- data.frame(x = c(1:1000), y = rnorm(1:1000))
head(old.df)

Define a new data frame called new.df

new.df <- data.frame(x = old.df[,1], z, y = old.df[,2])
head(new.df)

Here's a quick and dirty way of inserting a column in a specific position on a data frame. In my case, I have 5 columns in the original data frame: c1, c2, c3, c4, c5 and I will insert a new column c2b between c2 and c3.

1. Let's first create the test data frame:

   > dataset <- data.frame(c1 = 1:5, c2 = 2:6, c3=3:7, c4=4:8, c5=5:9) > dataset c1 c2 c3 c4 c5 1 1 2 3 4 5 2 2 3 4 5 6 3 3 4 5 6 7 4 4 5 6 7 8 5 5 6 7 8 9

2. Add the new column c2b at the end of our data frame:

   > dataset$c2b <- 10:14 > dataset c1 c2 c3 c4 c5 c2b 1 1 2 3 4 5 10 2 2 3 4 5 6 11 3 3 4 5 6 7 12 4 4 5 6 7 8 13 5 5 6 7 8 9 14

3. Reorder the data frame based on column indexes. In my case, I want to insert the new column (6) between existing columns 2 and 3. I do that by addressing the columns on my data frame using the vector c(1:2, 6, 3:5) which is equivalent to c(1, 2, 6, 3, 4, 5).

   > dataset <- dataset[,c(1:2, 6, 3:5)] > dataset c1 c2 c2b c3 c4 c5 1 1 2 10 3 4 5 2 2 3 11 4 5 6 3 3 4 12 5 6 7 4 4 5 13 6 7 8 5 5 6 14 7 8 9

There!

Easy solution. In a data frame with 5 columns, If you want insert another column between 3 and 4...

tmp <- data[, 1:3]
tmp$example <- NA # or any value.
data <- cbind(tmp, data[, 4:5]

For what it's worth, I wrote a function to do this:

[removed]

---

I have now updated this function with before and after functionality and defaulting place to 1. It also has data table compatability:

#####
# FUNCTION: InsertDFCol(colName, colData, data, place = 1, before, after)
# DESCRIPTION: Takes in a data, a vector of data, a name for that vector and a place to insert this vector into
# the data frame as a new column. If you put place = 3, the new column will be in the 3rd position and push the current
# 3rd column up one (and each subsuquent column up one). All arguments must be set. Adding a before and after
# argument that will allow the user to say where to add the new column, before or after a particular column.
# Please note that if before or after is input, it WILL override the place argument if place is given as well. Also, place
# defaults to adding the new column to the front.
#####

InsertDFCol <- function(colName, colData, data, place = 1, before, after) {
  
  # A check on the place argument.
  if (length(names(data)) < place) stop("The place argument exceeds the number of columns in the data for the InsertDFCol function. Please check your place number")
  if (place <= 0 & (!missing(before) | !(missing(after)))) stop("You cannot put a column into the 0th or less than 0th position. Check your place argument.")
  if (place %% 1 != 0 & (!missing(before) | !(missing(after)))) stop("Your place value was not an integer.")
  if (!(missing(before)) & !missing(after)) stop("You cannot designate a before AND an after argument in the same function call. Please use only one or the other.")
  
  # Data Table compatability.
  dClass <- class(data)
  data <- as.data.frame(data)
  
  # Creating booleans to define whether before or after is given.
  useBefore <- !missing(before)
  useAfter <- !missing(after)
  
  # If either of these are true, then we are using the before or after argument, run the following code.
  if (useBefore | useAfter) {
    
    # Checking the before/after argument if given. Also adding regular expressions.
    if (useBefore) { CheckChoice(before, names(data)) ; before <- paste0("^", before, "$") }
    if (useAfter) { CheckChoice(after, names(data)) ; after <- paste0("^", after, "$") }
    
    # If before or after is given, replace "place" with the appropriate number.
    if (useBefore) { newPlace <- grep(before, names(data)) ; if (length(newPlace) > 1) { stop("Your before argument matched with more than one column name. Do you have duplicate column names?!") }}
    if (useAfter) { newPlace <- grep(after, names(data)) ; if (length(newPlace) > 1) { stop("Your after argument matched with more than one column name. Do you have duplicate column names?!") }}
    if (useBefore) place <- newPlace # Overriding place.
    if (useAfter) place <- newPlace + 1 # Overriding place.
    
  }
  
  # Making the new column.
  data[, colName] <- colData
  
  # Finding out how to reorder this.
  # The if statement handles the case where place = 1.
  currentPlace <- length(names(data)) # Getting the place of our data (which should have been just added at the end).
  if (place == 1) {
    
    colOrder <- c(currentPlace, 1:(currentPlace - 1))
    
  } else if (place == currentPlace) { # If the place to add the new data was just at the end of the data. Which is stupid...but we'll add support anyway.
    
    colOrder <- 1:currentPlace
  
  } else { # Every other case.
    
    firstHalf <- 1:(place - 1) # Finding the first half on columns that come before the insertion.
    secondHalf <- place:(currentPlace - 1) # Getting the second half, which comes after the insertion.
    colOrder <- c(firstHalf, currentPlace, secondHalf) # Putting that order together.
    
  }
  
  # Reordering the data.
  data <- subset(data, select = colOrder)
  
  # Data Table compatability.
  if (dClass[1] == "data.table") data <- as.data.table(data)
  
  # Returning.
  return(data)
  
}

---

I realized I also did not include CheckChoice:

#####
# FUNCTION: CheckChoice(names, dataNames, firstWord == "Oops" message = TRUE)                                                                                               
# DESCRIPTION: Takes the column names of a data frame and checks to make sure whatever "choice" you made (be it 
# your choice of dummies or your choice of chops) is actually in the data frame columns. Makes troubleshooting easier. 
# This function is also important in prechecking names to make sure the formula ends up being right. Use it after 
# adding in new data to check the "choose" options. Set firstWord to the first word you want said before an exclamation point.
# The warn argument (previously message) can be set to TRUE if you only want to 
#####

CheckChoice <- function(names, dataNames, firstWord = "Oops", warn = FALSE) {
  
  for (name in names) {
    
    if (warn == TRUE) { if(!(name %in% dataNames)) { warning(paste0(firstWord, "! The column/value/argument, ", name, ", was not valid OR not in your data! Check your input! This is a warning message of that!")) } }
    if (warn == FALSE) { if(!(name %in% dataNames)) { stop(paste0(firstWord, "! The column/value/argument, " , name, ", was not valid OR not in your data! Check your input!")) } }
    
  }
}

I would simply use cbind() for this:

> df <- data.frame(a=1:5,
+                  b=10:14,
+                  c=rep(0,5),
+                  d=7:11)
> 
> z <- LETTERS[1:5]
> df <- cbind(df[,1:2], z, df[,3:4]) # Puts the z column between 2nd and 3rd column of df
> df
  a  b z c  d
1 1 10 A 0  7
2 2 11 B 0  8
3 3 12 C 0  9
4 4 13 D 0 10
5 5 14 E 0 11

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)   
  }

Here is a an example of how to move a column from last to first position. It combines [ with ncol. I thought it would be useful to have a very short answer here for the busy reader:

d = mtcars
d[, c(ncol(d), 1:(ncol(d)-1))] 

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")))

`

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

`

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.

You can do it like below -

df <- data.frame(a=1:4, b=5:8, c=9:12)
df['d'] <- seq(10,13)
df <- df[,c('a','b','d','c')]

df <- data.frame(a=c(1,2), b=c(3,4), c=c(5,6))
df %>%
  mutate(d= a/2) %>%
  select(a, b, d, c)

results

  a b   d c
1 1 3 0.5 5
2 2 4 1.0 6

I suggest to use dplyr::select after dplyr::mutate. It has many helpers to select/de-select subset of columns.

In the context of this question the order by which you select will be reflected in the output data.frame.

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