[R] merging two lists but get indexes

[Chuck Cleland]

Teng Sun wrote:
> Suppose I have two columns of entries, how can I get the union of the
> two columns? Please note: I input my columns through excel. These
> entries have text format in excel. Also, out of curiosity, how can I
> find out the data type of a data frame ?

df <- data.frame(n1 = c("apple","orange","soda","red","white",""),
                 n2 = c("soda","apple","green","yellow","blue","white"),
                 x = rnorm(6))

> str(df)
'data.frame':   6 obs. of  3 variables:
 $ n1: Factor w/ 6 levels "","apple","orange",..: 2 3 5 4 6 1
 $ n2: Factor w/ 6 levels "apple","blue",..: 4 1 3 6 2 5
 $ x : num  -0.0932 -2.0714 -0.9539  0.7249 -0.7039 ...

> lapply(df, class)
$n1
[1] "factor"

$n2
[1] "factor"

$x
[1] "numeric"

>> a <- read.csv("book1.csv")
>> a
>       n1     n2
> 1  apple   soda
> 2 orange  apple
> 3   soda  green
> 4    red yellow
> 5  white   blue
> 6         white
> 
>> union(a$n1,a$n2)
> [1] 2 3 5 4 6 1
> 
> I want the actual names instead of the indexes.

  You are getting the union of factor levels rather than the union of
the strings.  Try this:

> union(as.character(df$n1), as.character(df$n2))

[1] "apple"  "orange" "soda"
[4] "red"    "white"  ""
[7] "green"  "yellow" "blue"

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-- 
Chuck Cleland, Ph.D.
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