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?
218 Answers
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 
