[R] stumped on how to reorder factors

[Peter Alspach]

Tena koe Markus

I think you'll have to tailor a solution specific to your case.  However, the following might give you some ideas:

B <- as.factor(c("Engine 1", "Engine 10", "Ladder 3", "Engine 3", "Ladder 10", "Engine 10"))
summary(B)
 Engine 1 Engine 10  Engine 3 Ladder 10  Ladder 3 
        1         2         1         1         1 

ttMat <- as.data.frame(matrix(unlist(strsplit(as.character(B), ' ')), ncol=2, byrow=TRUE))
ttMat <- ttMat[order(ttMat[,1], as.numeric(as.character(ttMat[,2]))),]
B <- factor(B, levels=unique(apply(ttMat, 1, paste, collapse=' ')))
summary(B)
 Engine 1  Engine 3 Engine 10  Ladder 3 Ladder 10 
        1         1         2         1         1 

HTH ....

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Markus Weisner
> Sent: Wednesday, 31 August 2011 2:00 p.m.
> To: r-help at r-project.org
> Subject: [R] stumped on how to reorder factors
> 
> I am trying to reorder a factor data type so that when I plot stats
> associated with the factor, the ordering makes sense.
> 
> For instance, if I have a factor entered as follows ...
> 
> A = as.factor(c("1", "10", "3", "3", "10", "10"))
> 
> levels(A)
> 
> 
> ... the ordering does not really make sense (assuming I want the factor
> ordered by integer value), but I understand that this "mis-ordering"
> is
> because the ordering is based on a character string data type and not
> on an
> integer data type.  Because I run into this problem frequently, I wrote
> a
> small function to fix this:
> 
> 
> reorder_factor = function(x, x_sum, decreasing=FALSE){
> 
> factor(as.character(x), levels=levels(x)[order(x_sum,
> decreasing=decreasing)
> ])
> 
> }
> 
> 
> I can then run the following code to fix the problem:
> 
> 
> A = reorder_factor(x=A, x_sum=as.numeric(levels(A)), decreasing=FALSE)
> 
> levels(A)
> 
> 
> ... and now I have correctly ordered integers.  Perhaps not the most
> elegant
> solution, but it worked for my purposes.  Now I have a more complicated
> problem and I need help.  Assuming the following factor:
> 
> 
> B = as.factor(c("Engine 1", "Engine 10", "Ladder 3", "Engine 3",
> "Ladder 10",
> "Engine 10"))
> 
> levels(B)
> 
> 
> I would like the factor ordered first by the proceeding unit type and
> then
> ordered by the following integer.  In this case, I would like to see
> this
> order:  Engine 1, Engine 3, Engine 10, Ladder 3, Ladder 10.  I have
> tried
> many different ways of separating out the unit type from the number,
> but am
> having trouble figuring out a good way of achieving this factor order.
> For
> such a small example, I could obviously manually change the order, but
> I am
> dealing with much larger datasets with many unit types and up to 20
> different numbers for each unit type.  Having an automated way of
> ordering
> these units would be a huge help.  Thanks in advance for any help you
> can
> provide.
> 
> --Markus Weisner
> 
> 	[[alternative HTML version deleted]]
> 
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