A. Mani : Avoiding loops

mat<-matrix(sample(LETTERS[1:4], 200, replace=T),40,5)
df<-data.frame(mat)
table(df$X4)

Hi,
I'm not sure what you actually want from your email (following the
posting guide is a good way of helping you explain things to the rest
of us in a way we understand - it might even answer your question!

I'm only a beginner at R so no doubt one of our expert colleagues will
help me...

fred <- data.frame()
fred <- edit(fred)
fred

  A B C D E
1 1 2 X Y 1
2 2 3 G L 1
3 3 1 G L 5

fred[,3]

[1] X G G
Levels: G X

fred[fred[,3]=="G",]

  A B C D E
2 2 3 G L 1
3 3 1 G L 5

so at this point I can create a new dataframe with column 3 (C) ==
"G"; either explicitly or implicitly...

and if I want to calculate the sum() of column E, then I just say
something like...

sum(fred[fred[,3]=="G",][,5])

[1] 6

now naturally being a bit clueless at manipulating stuff in R, I
didn't know how to do this before I started... and you guys only get
to see the lines that I typed in and got a "successful" result...

according to section 6 of the "Introduction to R" manual which comes
with R, I could also have said > sum(fred[fred$C=="G",]$E) [1] 6

Hmmm.... I wonder would it be reasonable to put an example of this
type into section 2.7 of the "Introduction to R"?


cheers!
Sean


On 18/08/05, A. Mani <a_mani_sc_gs at vsnl.net> wrote:

Hello,
        I want to avoid loops in the following situation. There is a
        5-col
dataframe with col headers alone. two of the columns are
non-numeric. The problem is to calculate statistics(scores) for each
element of one column. The functions depend on matching in the other
non-numeric column.

A  B  C  E  F
1  2  X  Y  1
2  3  G  L  1
3  1  G  L  5
and so on ...30000+ entries.

I need scores for col E entries which depend on conditional
implications.


Thanks,

A. Mani
Member, Cal. Math. Soc