# [R] howto calculate column means in data frame

Joshua Wiley jwiley.psych at gmail.com
Sun Apr 10 17:36:16 CEST 2011

```Hi Jim,

Using ?lapply with ?colMeans should do the trick.  Here is a little sample:

eg <- list(mtcars, mtcars) # mtcars data frame twice in a list
resultsmean <- lapply(eg, colMeans) # calculate column means for each
element of "eg"
resultsmean # show the results

Hope this helps,

Josh

On Sun, Apr 10, 2011 at 8:27 AM, Maas James Dr (MED) <J.Maas at uea.ac.uk> wrote:
> Long story short, I have a big iterative procedure that produces a long list of data.frames such as the one called
> "results" here.  Is there an easy way to produce a similar list of data.frames comprised of the mean of each of the
> columns in results, such that it ends up like the one I've shown in "resultsmean" below?
>
> I've tried apply and lapply, still not got the correct arguments.  As usual, TIA.
>
> Jim
>
>> results
> [[1]]
>       name    LOR23       BIA23       MSE23          H0R23
> 1 0.2111122   -1.012228   -0.095937    0.035650        1.00
> 2 0.2111122   -0.836300    0.079991    0.042322        0.75
> 3 0.2111122   -0.518631    0.397659    0.214593        0.50
>
>
> [[2]]
>       name    LOR23       BIA23       MSE23          H0R23
> 1 0.2211122   -0.724630    0.191660    0.051308           1
> 2 0.2211122   -0.781812    0.134478    0.033872           1
> 3 0.2211122   -0.522109    0.394181    0.164628        0.75
>
>
> would like
>
>> resultsmean
> [[1]]
>       name    LOR23       BIA23       MSE23          H0R23
> 1 0.2111122   -0.78333    0.12734     0.097160        0.75
>
> [[2]]
>       name    LOR23       BIA23       MSE23          H0R23
> 1 0.2211122   -0.67566    0.2400      0.08266         0.916
>
> ===============================
> Dr. Jim Maas
> University of East Anglia
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

```