How can I add a column to a data frame such that the values added increase the total row count in R?

Question

I am new to R and want to add a column to an existing data frame with values. For example, say this is my current table

Column 1  |  Column 2  | Column 3
---------------------------------
Dog       |    Hound   |   Black
Doggo     |    Lab     |   Brown

I want to add another column such that the result would be this:

Column 1  |  Column 2  | Column 3 |  Column 4
---------------------------------------------
Dog       |    Hound   |   Black  |  Male
Dog       |    Hound   |   Black  |  Female
Doggo     |    Lab     |   Brown  |  Male
Doggo     |    Lab     |   Brown  |  Female

So it'd be almost like adding another dimension, but with a column. Any help would be appreciated!

Edit: found solution here https://stackoverflow.com/a/21911221/9882844

Second edit: Solution below in comment below is better actually

like this? df$column4 <- c("Male", "Female", "Male", Female") — giocomai, Jun 04 '18 at 21:42
expand grid doesn't work with data frames :/ @yeedlealso. The other solution doesn't work, it wants the amount of rows to be the same as before — Santi, Jun 04 '18 at 22:01
Possible duplicate of [Cartesian product data frame in R](https://stackoverflow.com/questions/4309217/cartesian-product-data-frame-in-r) — Bulat, Jun 04 '18 at 22:07

moodymudskipper · Accepted Answer · 2018-06-04T22:02:41.580

You can use merge with parameter all=TRUE:

df2 <- data.frame(Column4 = c("Male","Female"),stringsAsFactors = FALSE)

merge(df,df2,all = T)
#   Column1 Column2 Column3 Column4
# 1     Dog   Hound   Black    Male
# 2   Doggo     Lab   Brown    Male
# 3     Dog   Hound   Black  Female
# 4   Doggo     Lab   Brown  Female

You can also use crossing from tidyr library, which returns the order of your expected output:

tidyr::crossing(df,df2)
#   Column1 Column2 Column3 Column4
# 1     Dog   Hound   Black    Male
# 2     Dog   Hound   Black  Female
# 3   Doggo     Lab   Brown    Male
# 4   Doggo     Lab   Brown  Female

data

df <- read.table(text="Column1    Column2   Column3
Dog           Hound      Black
Doggo         Lab        Brown",h=T,strin=F)

How can I add a column to a data frame such that the values added increase the total row count in R?

1 Answers1