[R] assignment operator saving factor level as number

[Jeffrey Spies]

Glad you figured it out, but just be aware that if you set one value
of the column to be a character, it will make the whole vector
characters.  This could cause issues for analysis if you need numerics
or factors.  If the column is supposed to be a factor to begin with,
set it to be so; if you have two data frames, one with a column of
factors (dat2) and one with what should be a column of factors (dat1),
you can use something like this:

dat1$columnThatShouldBeFactors <- as.factor(
    dat1$columnThatShouldBeFactors,
    levels=levels(dat2$columnThatIsAlreadyFactors)
)

Cheers,

Jeff.

On Fri, Nov 5, 2010 at 6:03 PM, Wade Wall <wade.wall at gmail.com> wrote:
> Hi all,
>
> Thanks for the help.  Jeffrey was right; my initial dataframe did not have
> the columns defined for factors.  I solved it using Jorge's example of using
> as.character.
>
> Sorry for not being more clear before.
>
> Wade
>
> On Fri, Nov 5, 2010 at 4:12 PM, Jeffrey Spies <jspies at virginia.edu> wrote:
>>
>> Perhaps this will help:
>>
>> > test1 <- test2 <- data.frame(col1=factor(c(1:3), labels=c("a", "b",
>> > "c")))
>> > test3 <- data.frame(col1 = 1:3)
>>
>> Now:
>>
>> > test2[2,1] <- test1$col1[1]
>> > test2$col1
>> [1] a a c
>> Levels: a b c
>>
>> vs
>>
>> > test3[2,1] <- test1$col1[1]
>> > test3$col1
>> [1] 1 1 3
>>
>> Because test3's first column, col1, is a vector of numeric, and each
>> element of a vector must have the same data type (numeric, factor,
>> etc), it will coerce the data coming in to have the same data type (if
>> it can).  In this case, the data type is numeric.  Had it been a
>> character coming in, because it can't coerce a character to a numeric,
>> it would have made the entire vector a vector of characters:
>>
>> > test3[2,1] <- 'b'
>> > test3$col1
>> [1] "1" "b" "3"
>>
>> Hope that demonstrates what's probably going on,
>>
>> Jeff.
>>
>> On Fri, Nov 5, 2010 at 3:54 PM, Wade Wall <wade.wall at gmail.com> wrote:
>> > Hi all,
>> >
>> > I have a dataframe (df1) that I am trying to select values from to a
>> > second
>> > dataframe that at the current time is only for the selected items from
>> > df1
>> > (df2).  The values that I am trying to save from df1 are factors with
>> > alphanumeric names
>> >
>> > df1 looks like this:
>> >
>> > 'data.frame':   3014 obs. of  13 variables:
>> >  $ Num         : int  1 1 1 2 2 2 3 3 3 4 ...
>> >  $ Tag_Num     : int  1195 1195 1195 1162 1162 1162 1106 1106 1106 1173
>> > ...
>> >  $ Site        : Factor w/ 25 levels "PYBR002A","PYBR003B",..: 1 1 1 1 1
>> > 1 1
>> > 1 1 1 ...
>> >  $ Site_IndNum : Factor w/ 1044 levels "PYBR002A_001",..: 1 1 1 2 2 2 3
>> > 3 3
>> > 4 ...
>> >  .... ...
>> >  $ Area        : num  463.3 29.5 101.8 152.9 34.6 ...
>> >
>> > However, whenever I try to assign values, like this
>> >
>> > df2[j,1]<-df2$Site[i]
>> >
>> > the values are changed from alphanumeric (e.g. PYBR003A) to numerals
>> > (e.g.
>> > 1).
>> >
>> > Does anyone know why this is happening and how I can assign the actual
>> > values from df1 to df2?
>> >
>> > Thanks in advance,
>> >
>> > Wade
>> >
>> >        [[alternative HTML version deleted]]
>> >
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>> >
>
>