[R] Average every 4 columns

Wed Nov 9 18:36:24 CET 2016

> On Nov 9, 2016, at 9:24 AM, David Winsemius <dwinsemius at comcast.net> wrote:
> 
> 
>> On Nov 9, 2016, at 9:00 AM, Miluji Sb <milujisb at gmail.com> wrote:
>> 
>> Thanks a lot for your quick reply. I made a mistake in the question, I
>> meant to ask every 4 (or 12) rows not columns. Apologies. Thanks again!
> 
> Then try matrix( sapply( split( x , 0:(dim(x)[2]/4-1)*4+1] ), mean) 
> 
> Again assuming that dim(x)[1] is evenly divisible by 4. (It's not clear if you wanted these means "within columns" or "blocks defined by rows". This is lightly tested but should provide the latter. 
> 
> sapply( split ( unlist(x) , 0:(dim(x)[2]/4-1)*4+1 ), mean)
>       1        5        9 
> 19.44819 19.22003 19.12812 

I failed to understand Daniel's logic an blindly copied his sequence which was not what I thought it would produce. 

Your request for "every 4" seems problematic in that your example has 10 rows and you haven't said what to do with the "bottom" 2 rows.

-- 
David
> 
>> 
>> Sincerely,
>> 
>> Milu
>> 
>> On Wed, Nov 9, 2016 at 5:45 PM, Dalthorp, Daniel <ddalthorp at usgs.gov> wrote:
>> 
>>> Hi Milu,
>>> The following should work for an array x (provided dim(x)[2] is divisible
>>> by 4):
>>> 
>>> colMeans(x[,
>>> 
>>> -Dan
>>> 
>>> On Wed, Nov 9, 2016 at 8:29 AM, Miluji Sb <milujisb at gmail.com> wrote:
>>> 
>>>> Dear all,
>>>> 
>>>> I have a dataset with hundreds of columns, I am only providing only 12
>>>> columns. Is it possible to take the mean of every four (or 12) columns
>>>> (value601, value602, value603, value604 etc.in this case) and repeat for
>>>> the hundreds of columns? Thank you.
>>>> 
>>>> Sincerely,
>>>> 
>>>> Milu
>>>> 
>>>> structure(list(value601 = c(10.1738710403442, 3.54112911224365,
>>>> 12.9192342758179, 3.17447590827942, 11.7332258224487, 7.68282270431519,
>>>> -7.11564493179321, 0.987620949745178, 13.0476207733154, 6.36939525604248
>>>> ), value602 = c(13.0642414093018, 5.53129482269287, 16.0519638061523,
>>>> 2.88946437835693, 14.9204912185669, 9.42428588867188, -6.80674123764038,
>>>> -0.614241063594818, 16.7947769165039, 7.9541072845459), value603 =
>>>> c(22.0399188995361,
>>>> 14.398024559021, 24.9523792266846, 12.0878629684448, 23.6459674835205,
>>>> 18.3277816772461, -2.54092741012573, 10.5550804138184, 25.1016540527344,
>>>> 16.2166938781738), value604 = c(27.7165412902832, 20.3255825042725,
>>>> 30.8430004119873, 16.6856250762939, 29.2485408782959, 24.3775005340576,
>>>> 6.47758340835571, 15.5897912979126, 30.7387924194336, 22.3637084960938
>>>> ), value605 = c(31.6644763946533, 23.4093952178955, 35.1488723754883,
>>>> 19.7132263183594, 33.3924179077148, 29.5846366882324, 10.2083873748779,
>>>> 19.3551616668701, 35.3076629638672, 27.4299201965332), value606 =
>>>> c(33.9698333740234,
>>>> 26.8574161529541, 36.8900833129883, 22.8604583740234, 34.8642921447754,
>>>> 33.8158760070801, 14.7055835723877, 22.1144580841064, 37.0545425415039,
>>>> 32.1087913513184), value607 = c(36.0279846191406, 26.9297180175781,
>>>> 38.2701225280762, 23.2643146514893, 36.7398796081543, 34.1216125488281,
>>>> 17.1387901306152, 24.0419750213623, 37.8542327880859, 32.7677421569824
>>>> ), value608 = c(34.0242347717285, 25.7720966339111, 36.4897193908691,
>>>> 22.0332260131836, 34.8011703491211, 32.6856842041016, 16.6232261657715,
>>>> 21.5571365356445, 36.1491546630859, 31.1716938018799), value609 =
>>>> c(27.5402088165283,
>>>> 21.7590408325195, 30.5214176177979, 18.4252090454102, 29.1156253814697,
>>>> 26.9878330230713, 12.4962501525879, 17.7259578704834, 30.9099159240723,
>>>> 25.4832077026367), value610 = c(23.4706859588623, 17.0126209259033,
>>>> 26.8166942596436, 15.297459602356, 25.1733055114746, 23.5616931915283,
>>>> 8.86995983123779, 13.5793552398682, 27.5732250213623, 22.1691932678223
>>>> ), value611 = c(14.5820417404175, 9.08279132843018, 17.8419170379639,
>>>> 8.36016654968262, 16.5633754730225, 14.8123331069946, 1.32095837593079,
>>>> 5.73408317565918, 18.9752082824707, 13.5729999542236), value612 =
>>>> c(9.12979793548584,
>>>> 2.79943537712097, 11.6504030227661, 2.21584677696228, 10.5404834747314,
>>>> 7.55471754074097, -5.58141136169434, -0.566209673881531, 12.3264112472534,
>>>> 6.65576601028442)), .Names = c("value601", "value602", "value603",
>>>> "value604", "value605", "value606", "value607", "value608", "value609",
>>>> "value610", "value611", "value612"), row.names = c("1", "2",
>>>> "3", "4", "5", "6", "7", "8", "9", "10"), class = "data.frame")
>>>> 
>>>>       [[alternative HTML version deleted]]
>>>> 
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide http://www.R-project.org/posti
>>>> ng-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>> 
>>>> 
>>> 
>>> 
>>> --
>>> Dan Dalthorp, PhD
>>> USGS Forest and Rangeland Ecosystem Science Center
>>> Forest Sciences Lab, Rm 189
>>> 3200 SW Jefferson Way
>>> Corvallis, OR 97331
>>> ph: 541-750-0953
>>> ddalthorp at usgs.gov
>>> 
>>> 
>> 
>> 	[[alternative HTML version deleted]]
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> 
> David Winsemius
> Alameda, CA, USA
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius
Alameda, CA, USA