Map array of strings to an array of integers

Question

Suppose I have a column in a data frame as colors say c(\"Red\", \"Blue\", \"Blue\", \"Orange\"). I would like to get it as c(1,2,2,3).

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Answer 1

I must be missing something, but this method would work I believe. Having coerced your column with words (below, "names") to a factor, you revalue them by your numbers in "colors".

require(plyr)

colors <- c("1","2","3")
names <- c("Red", "Blue", "Orange")
df <- data.frame(names, colors)
df$names <- as.factor(df$names)
df$names <- revalue(x = df$names, c("Red" = 1, "Blue" = 2, "Orange" = 3))

Answer 2

Set up a named vector, describing the link between colour and integers (i.e. specifically how the strings map to the integers):

colors=c(1,2,3)
names(colors)=c("Red", "Blue", "Orange")

Now use the named vector to generate a list of numbers associated with the colours in your data frame:

>colors[c("Red","Blue","Blue","Orange")]
   Red   Blue   Blue Orange 
     1      2      2      3 

UPDATE to address questions below. Here's an example of what I think you're trying to do.

dataframe=data.frame(Gender=c("F","F","M","F","F","M"))
strings=sort(unique(dataframe$Gender))
colors=1:length(strings)
names(colors)=strings
dataframe$Colours=colors[dataframe$Gender]

Can have a look at the result:

> dataframe
  Gender Colours
1      F      1
2      F      1
3      M      2
4      F      1
5      F      1
6      M      2

Note that this example assumes that you have no specific mapping between Gender and Colours in mind. If this is really the case, then it might be simpler to just follow the comment from @alexis_laz instead.

Answer 3

Here is a function based on previous code:

# Recode 'string' into 'integer'
recode_str_int <- function(df, feature) {

  # 1. Unique values

  # 1.1. 'string' values
  list_str <- sort(unique(df[, feature]))

  # 1.2. 'integer' values
  list_int <- 1:length(list_str)

  # 2. Create new feature

  # 2.1. Names
  names(list_int) = list_str
  df$feature_new = list_int[df[, feature]]

  # 3. Result
  df$feature_new

} # recode_str_int

Call it like:

 df$new_feature <- recode_str_int(df, "feature")

Answer 4

Using car::recode() function:

library(car)

recode(x, "'Red'=1; 'Blue'=2; 'Orange'=3;")
# [1] 1 2 2 3