# [R] How to avoid conversion to factors (data frame to zoo)

Gabor Grothendieck ggrothendieck at gmail.com
Thu Oct 18 17:16:15 CEST 2007

```A zoo variable is a vector or matrix with an index so you can't
mix types (factors and numeric) in a single zoo variable; however,
you can represented the factor numerically:

library(zoo)
set.seed(1)
a <- data.frame(
nn = letters[1:4],
dd = as.Date("2007-08-01") + 1:4,
x = rnorm(4),
y = rnorm(4)
)

z <- zoo(data.matrix(a[-2]), a\$dd)
z

# or you can put the factor in a second zoo variable:

z2 <- zoo(as.matrix(a[3:4]), a\$dd)
zf <- zoo(a\$nn, a\$dd)
z2
zf

On 10/18/07, Li, Yan (IED) <Yan.Y.Li at morganstanley.com> wrote:
> Hi all,
>
> I was trying to convert a data frame to a zoo object so I can use some
> time series functions like lag(). But it seems then everything became a
> factor, so I have to convert it back to numeric to run the correct
> regressions. Is there a way to avoid it? Here is an example:
>
> #############################
> a <- data.frame(nn =as.character(c("a", "b", "c", "d")), dd =
> as.Date("2007-08-01")+ c(1,2,3,4), x = rnorm(4), y = rnorm(4))
> a
> str(a)
>
>
> b <- zoo(a, order.by = a\$dd)
> b
> str(b)
>
> c <- data.frame(b)
> str(c)
>
> #############################################333
> Results of this example:
> > a
>  nn         dd      x      y
> 1  a 2007-08-02  0.388 -0.394
> 2  b 2007-08-03 -0.054 -0.059
> 3  c 2007-08-04 -1.377  1.100
> 4  d 2007-08-05 -0.415  0.763
> > str(a)
> 'data.frame':   4 obs. of  4 variables:
>  \$ nn: Factor w/ 4 levels "a","b","c","d": 1 2 3 4
>  \$ dd:Class 'Date'  num [1:4] 13727 13728 13729 13730
>  \$ x : num   0.3877 -0.0538 -1.3771 -0.4150
>  \$ y : num  -0.3943 -0.0593  1.1000  0.7632
> > b <- zoo(a, order.by = a\$dd)
> > b
>           nn dd         x      y
> 2007-08-02 a  2007-08-02  0.388 -0.394
> 2007-08-03 b  2007-08-03 -0.054 -0.059
> 2007-08-04 c  2007-08-04 -1.377  1.100
> 2007-08-05 d  2007-08-05 -0.415  0.763
> > str(b)
>  chr [1:4, 1:4] "a" "b" "c" "d" "2007-08-02" "2007-08-03" ...
>  - attr(*, "dimnames")=List of 2
>  ..\$ : chr [1:4] "1" "2" "3" "4"
>  ..\$ : chr [1:4] "nn" "dd" "x" "y"
>  - attr(*, "index")=Class 'Date'  num [1:4] 13727 13728 13729 13730
> >
> > c <- data.frame(b)
> > str(c)
> 'data.frame':   4 obs. of  4 variables:
>  \$ nn: Factor w/ 4 levels "a","b","c","d": 1 2 3 4
>  ..- attr(*, "names")= chr  "1" "2" "3" "4"
>  \$ dd: Factor w/ 4 levels "2007-08-02","2007-08-03",..: 1 2 3 4
>  ..- attr(*, "names")= chr  "1" "2" "3" "4"
>  \$ x : Factor w/ 4 levels " 0.388","-0.054",..: 1 2 4 3
>  ..- attr(*, "names")= chr  "1" "2" "3" "4"
>  \$ y : Factor w/ 4 levels " 0.763"," 1.100",..: 4 3 2 1
>  ..- attr(*, "names")= chr  "1" "2" "3" "4"
> ##################################3
> So after converting to zoo, all the variables became factors. How can I
> keep this from happening? Thank you very much for any advice.
>
> Yan
> --------------------------------------------------------
>
> This is not an offer (or solicitation of an offer) to bu...{{dropped:22}}
>
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