[R] best way to aggregate / rearrange data.frame with different data types

[Dennis Murphy]

Hi:

Here's another approach using the plyr and reshape packages. (There
are multiple ways to do this, BTW.)

## (1)
library(plyr)
> ddply(dat, .(Subject, gender, comment), summarise, mean_y = mean(y))
  Subject gender   comment   mean_y
1       1      w comment A 3.881864
2       2      m comment B 2.213656
3       3      w comment C 2.568794

## (2)
# Add a 'time' variable holding names to associate to new columns
dat$time <- paste('y', rep(1:4, 3), sep = '')

# reshape from 'long' to 'wide' form
cast(dat, Subject + gender + comment ~ time, value = 'y')
  Subject gender   comment        y1       y2       y3       y4
1       1      w comment A 5.9299385 3.268402 2.634573 3.694540
2       2      m comment B 2.0663910 1.475625 1.960885 3.351722
3       3      w comment C 0.6656096 3.044818 4.833166 1.731582

HTH,
Dennis

On Mon, Jul 11, 2011 at 8:55 AM, Martin Batholdy
<batholdy at googlemail.com> wrote:
> Hi,
>
>
> I have a data.frame that looks like this:
>
>
> Subject <- c(rep(1,4), rep(2,4), rep(3,4))
> y <- rnorm(12, 3, 2)
> gender <- c(rep("w",4), rep("m",4), rep("w",4))
> comment <- c(rep("comment A",4), rep("comment B",4), rep("comment C",4))
>
> data <- data.frame(Subject,y,gender,comment)
> data
>
>   Subject           y gender   comment
> 1        1  2.86495339      w comment A
> 2        1  3.33758993      w comment A
> 3        1  7.00301094      w comment A
> 4        1  3.81585998      w comment A
> 5        2  2.50300460      m comment B
> 6        2 4.93830489      m comment B
> 7        2 5.08184289      m comment B
> 8        2  4.00552691      m comment B
> 9        3 3.16131181      w comment C
> 10       3  4.61620021      w comment C
> 11       3 3.68288799      w comment C
> 12       3 -0.05049953      w comment C
>
>
>
> So I have multiple lines for one subject because of a repeated measurement of variable y
> (the rest of the variables stay the same, like gender).
>
>
> Now I would like to transform this data.frame in two ways:
>
> 1. a aggregated form,
> where I only have one row left for each subject - for numerical variables within the data.frame (like y) a mean should be calculated.
>
>
> 2. a restructured form,
> where I only have one row for each subject, but four different y-columns (y1, y2, y3, y4).
>
>
> What is the easiest way to do this?
> Are there any functions who do this kind of data-frame rearranging in one step?
>
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