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I have a data frame with 1 vector of integers and 1 as a character factor like so:

enter image description here

I have created a linear model that shows a relationship between age and party affiliation. I now want to determine the best bins of ages (50-59, 60-69, etc..) that can explain party affiliation. Is there an R package/model that can help me do that?

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    $\begingroup$ I would suggest not binning a continuous variable since this is needlessly throwing away information in general. Can you explain your actual model? You seem to have a class variable with several levels as the response, so how did you fit a linear model? $\endgroup$
    – dsaxton
    Commented Aug 11, 2015 at 2:16
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    $\begingroup$ Simply asking for functions / packages is off topic here. You may want to look into Fisher's Linear Discriminant Analysis (Quick-R), though. $\endgroup$
    – gung - Reinstate Monica
    Commented Aug 11, 2015 at 2:26

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You might try a regression tree with party as response and age as independent variable. 

>temp <- rpart(Party ~ Age)
>plot(temp)
>text(temp)

The algorithm will find suitable places to split the Age variable, if these exist. If not, the tree won't grow past the root stage, which would tell you something.

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(For the record, I agree with @dsaxton. But just to give you something, here is a quick demonstration of using LDA to optimally bin a continuous variable based on a factor.) 

library(MASS)

Iris  = iris[,c(1,5)]
model = lda(Species~Sepal.Length, Iris)
range(Iris$Sepal.Length)  # [1] 4.3 7.9
cbind(seq(4, 8, .1), 
      predict(model, data.frame(Sepal.Length=seq(4, 8, .1)))$class)
#       [,1] [,2]
#  [1,]  4.0    1
#  [2,]  4.1    1
#        ...
# [15,]  5.4    1
# [16,]  5.5    2
# [17,]  5.6    2
#        ...
# [23,]  6.2    2
# [24,]  6.3    3
# [25,]  6.4    3
#        ...
# [41,]  8.0    3
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    $\begingroup$ Neat idea. I'm not sure if there is a universal equivalence, but making the class predictions via a multinomial model results in the same predictions for your Iris example. Example here. That has an example plot to show uncertainty in the predictions as well. $\endgroup$
    – Andy W
    Commented Aug 11, 2015 at 13:10
  • $\begingroup$ @AndyW, they are similar but won't be universally equivalent. LDA assumes age is normally distributed; if so, it will work slightly better--especially as the distributions get further apart. MLR can handle categorical variables (sex, race, etc) as well, so can be more generally applicable, but it seems to me a little more advanced to understand & use (although your example was very straightforward, so maybe not). MLR is a viable option; you could add it as an answer, if you wanted. $\endgroup$
    – gung - Reinstate Monica
    Commented Aug 13, 2015 at 1:11

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