CODEWITHSUNDEEP
r
steven
steven

Reputation: 683

Replace factors with a numeric value

I have a data frame where each column is of type factor and has over 3000levels. Is there a way where I can replace each level with a numeric value. Consider the inbuilt data frame InsectSprays

> str(InsectSprays)
'data.frame':   72 obs. of  2 variables:
 $ count: num  10 7 20 14 14 12 10 23 17 20 ...
 $ spray: Factor w/ 6 levels "A","B","C","D",..: 1 1 1 1 1 1 1 1 1 1 ...

The replacement should be as follows:

A=1,B=2,C=3,D=4,E=5,F=6.

If there are 3000 levels:

"USA"=1,"UK"=2....,France="3000".

The solution should automatically detect the levels(Ex: 3000),then replace each level starting from 1 to 3000.

Upvotes: 3

Views: 16547

Answers (3)

MKob
MKob

Reputation: 11

Based on this tutorial (https://statisticsglobe.com/how-to-convert-a-factor-to-numeric-in-r/), I have used the following code to convert factor levels into specific numbers:

levels(InsectSprays$spray) # to check the order levels are stored

levels(InsectSprays$spray) <- c(0, 1, 2, 3, 4, 5) # assign the number I want to each level 

InsectSprays$spray <- as.numeric(as.character(InsectSprays$spray)) # to change from factor to numeric

Upvotes: 1

eipi10
eipi10

Reputation: 93761

Factor variables already have underlying numeric values corresponding to each factor level. You can see this as follows:

as.numeric(InsectSprays$spray)

or

x = factor(c("A","D","B","G"))
as.numeric(x)

If you want to add specific numeric values corresponding to each level, you can, for example, merge in those values from a lookup table:

# Create a lookup table with the numeric values you want to correspond to each level of spray
lookup = data.frame(spray=levels(InsectSprays$spray), sprayNumeric=c(5,4,1,2,3,6))

# Merge lookup values into your data frame
InsectSprays = merge(InsectSprays, lookup, by="spray")

Upvotes: 6

Joel Carlson
Joel Carlson

Reputation: 640

For the InsectSprays example, you can use:

levels(InsectSprays$spray) <- 1:6

Should generalize to your problem.

Upvotes: 7

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