[R] merging dataframes in a list

[Ulrik Stervbo]

You can use ldply in the plyr package to bind all the data.frames together
(a regular loop will also work). Afterwards you can summarise using ddply

Hope this helps
Ulrik

Ed Siefker <ebs15242 at gmail.com> schrieb am Fr., 3. Juni 2016 21:10:

> aggregate isn't really what I want.  Maybe tapply?  I still can't get
> it to work.
>
> > length(mylist)
> [1] 4
> > length(names)
> [1] 4
> > tapply(mylist, names, merge)
> Error in tapply(mylist, names, merge) : arguments must have same length
>
> I guess because a list isn't an atomic data type.  What function will
> do the same on lists?  lapply doesn't have a 'by' argument.
>
> On Fri, Jun 3, 2016 at 1:41 PM, Ed Siefker <ebs15242 at gmail.com> wrote:
> > I manually constructed the list of sample names and tried the
> > aggregate call I mentioned.
> > Merge works when called manually, but not when using aggregate.
> >
> >> mylist <- list(data.frame(name="sample1", red=20),
> data.frame(name="sample1", green=15), data.frame(name="sample2", red=10),
> data.frame(na me="sample2", green=30))
> >>  names <- list("sample1", "sample1", "sample2", "sample2")
> >> merge(mylist[1], mylist[2])
> >      name red green
> > 1 sample1  20    15
> >> merge(mylist[3], mylist[4])
> >      name red green
> > 1 sample2  10    30
> >> aggregate(mylist, by=as.list(names), merge)
> > Error in as.data.frame(y) : argument "y" is missing, with no default
> >
> > What's the right way to do this?
> >
> > On Fri, Jun 3, 2016 at 1:20 PM, Ed Siefker <ebs15242 at gmail.com> wrote:
> >> I have a list of data as follows.
> >>
> >>> list(data.frame(name="sample1", red=20), data.frame(name="sample1",
> green=15), data.frame(name="sample2", red=10), data.frame(name="sample 2",
> green=30))
> >> [[1]]
> >>      name red
> >> 1 sample1  20
> >>
> >> [[2]]
> >>      name green
> >> 1 sample1    15
> >>
> >> [[3]]
> >>      name red
> >> 1 sample2  10
> >>
> >> [[4]]
> >>      name green
> >> 1 sample2    30
> >>
> >>
> >> I would like to massage this into a data frame like this:
> >>
> >>      name red green
> >> 1 sample1  20    15
> >> 2 sample2  10    30
> >>
> >>
> >> I'm imagining I can use aggregate(mylist, by=samplenames, merge)
> >> right?  But how do I get the list of samplenames?  How do I subset
> >> each dataframe inside the list?
>
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