Export data frame as factors

Question

New to R and first post here - this might be really obvious but I must be missing something.

Imported a csv with a binary dependent while

purchase=read.csv("../Desktop/purchase.csv", stringsASfactors=TRUE)

Now I wish to export the same data frame from R (in .csv), but instead keep the categorical variables (which were originally strings) as factors, effectively converting the data set.

I tried

write.csv(purchase,'../Desktop/purchaseconverted.csv', stringsASfactors=TRUE) 

but the write function doesn't support stringsASfactors.

I welcome help!

Answer 1

Using the factor() function, you can cast a vector as a categorical variable directly. Then write to csv.

purchase <- data.frame(a,b,c)
purchase['a'] <- factor(a)

write.csv(purchase,'../Desktop/purchaseconverted.csv')

Hope this helps.

Answer 2

The default behavior is going to treat factors as character strings when writing them to file. See this in the below example using the iris dataset, which contains a factor column Species :

write.csv(head(iris))
# "","Sepal.Length","Sepal.Width","Petal.Length","Petal.Width","Species"
# "1",5.1,3.5,1.4,0.2,"setosa"
# "2",4.9,3,1.4,0.2,"setosa"
# "3",4.7,3.2,1.3,0.2,"setosa"
# "4",4.6,3.1,1.5,0.2,"setosa"
# "5",5,3.6,1.4,0.2,"setosa"
# "6",5.4,3.9,1.7,0.4,"setosa"

You can change this by converting the factors to numeric, so the file contains the numeric values rather than the factor labels for the factor variable:

iris2 <- iris
iris2$Species <- as.numeric(iris2$Species)
> write.csv(head(iris2))
# "","Sepal.Length","Sepal.Width","Petal.Length","Petal.Width","Species"
# "1",5.1,3.5,1.4,0.2,1
# "2",4.9,3,1.4,0.2,1
# "3",4.7,3.2,1.3,0.2,1
# "4",4.6,3.1,1.5,0.2,1
# "5",5,3.6,1.4,0.2,1
# "6",5.4,3.9,1.7,0.4,1

This way you write the factor values, not the factor labels, to the CSV.