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I have a DF where I want to add a new variable called "B" into the 2nd position.
A C D
1 1 5 2
2 3 3 7
3 6 2 3
4 6 4 8
5 1 1 2
Anyone have an idea?
795
In this example, instead of using the assign() method, we use square brackets ([]) to create a new variable or column for an existing Dataframe. The syntax goes like this: dataframe_name['column_name'] = data column_name is the name of the new column to be added in our dataframe.
In pandas you can add/append a new column to the existing DataFrame using DataFrame. insert() method, this method updates the existing DataFrame with a new column. DataFrame. assign() is also used to insert a new column however, this method returns a new Dataframe after adding a new column.
The easiest way would be to add the columns you want and then reorder them:
dat$B <- 1:5
newdat <- dat[, c("A", "B", "C", "D")]
Another way:
newdat <- cbind(dat[1], B=1:5, dat[,2:3])
If you're concerned about overhead, perhaps a data.table solution? (With help from this answer):
library(data.table)
dattable <- data.table(dat)
dattable[,B:=1:5]
setcolorder(dattable, c("A", "B", "C", "D"))
dat$B <- 1:5
ind <- c(1:which(names(data) == "A"),ncol(data),(which(names(data) == "A")+1):ncol(data)-1)
data <- data[,ind]
Create the variable at the end of the data.frame and then using an indicator vector signaling how to reorder the columns. ind is just a vector of numbers
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