[R] rowMean, specify subset of columns within Dataframe?

[aaront]

Thank you all. 

So that I look up the relevant Help topic more fully, the part that extracts
the columns of interest: 
[, c(1, 3:4)]

is this an instance of ?Subscript which Charles directs me to?   

Cheers, Aaron 


Bill.Venables wrote:
> 
> Suppose you want to select column 1, 3 and 4 only.
> 
> ### you don't need the cbind(...) here
> Data1 <- data.frame(I1 = 3, I2 = c(0, 3:1, 2:5, NA),
>           I3 = c(1:4, NA, 5:2), I4 = 2, I5 = 3)
> 
> Data1$mean_134 <- rowMeans(Data1[, c(1, 3:4)], na.rm = TRUE)
> Data1
> 
> Bill Venables.
> 
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of aaront
> Sent: Monday, 26 November 2007 6:02 AM
> To: r-help at r-project.org
> Subject: [R] rowMean, specify subset of columns within Dataframe?
> 
> 
> I would like to calculate the mean of tree leader increment growth over
> 5
> years (I1 through I5) where each tree is a row and each row has 5
> columns.
> So far I have achieved this using rowMeans when all columns are numeric
> type
> and used in the calculation:
> 
> Data1 <- data.frame(cbind(I1 = 3, I2 = c(0,3:1, 2:5,NA), I3
> =c(1:4,NA,5:2),I4=2,I5=3))
> Data1
> Data1$mean_5 <- rowMeans(Data1, na.rm =T)
> Data1
> 
> My real dataset has many columns including several Factor type. Is it
> possible to specify a range of columns within a data frame  using
> rowMeans
> dims= (say where there is a one 
> Factor  column called Species leading I1 to I5, and one Factor column
> called
> Moisture following, so 7 columns total) , or do I either need to extract
> those columns to a new data frame, calculate means, and reattach to the
> original data frame, or use a different function such as apply?
> 
> Unfortunately I am fairly new to R and have a difficult time with some
> terminology and concepts in R Help.
> 
> -- 
> View this message in context:
> http://www.nabble.com/rowMean%2C-specify-subset-of-columns-within-Datafr
> ame--tf4871420.html#a13939204
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
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> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide
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> 
> 

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