[R] converting "by" to a data.frame?

[Sundar Dorai-Raj]

Spencer,
   Would "sapply" be better here?

R> by.df <- data.frame(A=rep(c("A1", "A2"), each=3),
R+                     B=rep(c("B1", "B2"), each=3),
R+                     x=1:6, y=rep(0:1, length=6))
R> t(sapply(split(by.df, do.call("paste", c(by.df[, 1:2], sep = ":"))),
R+          function(x) coef(lm(y ~ x, data = x))))
       (Intercept)             x
A1:B1   0.3333333 -1.517960e-16
A2:B2   0.6666667  3.282015e-16
R>

Sundar

Spencer Graves wrote:
> Hi, Thomas, et al.:
> 
> Thanks for the reply.  Unfortunately, "do.call" strips off the subset 
> identifiers, which I want to use for further modeling:
> 
>  > do.call("rbind", byFits)
>      (Intercept)              x
> [1,]   0.3333333 -1.517960e-016
> [2,]   0.6666667  3.282015e-016
> 
> The following does what I want using a "for" loop:
> 
>  > by.df <- data.frame(A=rep(c("A1", "A2"), each=3),
> +  B=rep(c("B1", "B2"), each=3), x=1:6, y=rep(0:1, length=6))
>  > by.lvls <- paste(as.character(by.df$A), as.character(by.df$B), sep=":")
>  > A.B <- unique(by.lvls)
>  > Fits <- data.frame(A.B = A.B, .Intercept.=rep(NA, length(A.B)),
> +  x=rep(NA, length(A.B)))
>  > Fits$A <- substring(A.B, 1, regexpr(":", A.B)-1)
>  > Fits$B <- substring(A.B, regexpr(":", A.B)+1)
>  > for(i in 1:length(A.B))
> +  Fits[i, 2:3] <- coef(lm(y~x, by.df[by.lvls==A.B[i],]))
>  > Fits
>     A.B X.Intercept.             x  A  B
> 1 A1:B1    0.3333333 -1.517960e-16 A1 B1
> 2 A2:B2    0.6666667  3.282015e-16 A2 B2
>  >
> 
>       I wondered if there was something easier.
> 
> Thanks again for your reply.
> Spencer Graves
> 
> Thomas Lumley wrote:
> 
>> On Thu, 5 Jun 2003, Spencer Graves wrote:
>>
>>
>>> Dear R-Help:
>>>
>>>       I want to (a) subset a data.frame by several columns, (b) fit a 
>>> model
>>> to each subset, and (c) store a vector of results from the fit in the
>>> columns of a data.frame.  In the past, I've used "for" loops do do this.
>>>  Is there a way to use "by"?
>>>
>>>       Consider the following example:
>>>
>>> > byFits <- by(by.df, list(A=by.df$A, B=by.df$B),
>>> +  function(data.)coef(lm(y~x, data.)))
>>> > byFits
>>> A: A1
>>> B: B1
>>>   (Intercept)             x
>>>  3.333333e-01 -1.517960e-16
>>> ------------------------------------------------------------
>>> A: A2
>>> B: B1
>>> NULL
>>> ------------------------------------------------------------
>>> A: A1
>>> B: B2
>>> NULL
>>> ------------------------------------------------------------
>>> A: A2
>>> B: B2
>>>  (Intercept)            x
>>> 6.666667e-01 3.282015e-16
>>> >
>>> >
>>> #############################
>>> Desired output:
>>>
>>> data.frame(A=c("A1","A2"), B=c("B1", "B2"),
>>>     .Intercept.=c(1/3, 2/3), x=c(-1.5e-16, 3.3e-16))
>>>
>>> What's the simplest way to do this?
>>
>>
>>
>> do.call("rbind", byFits)
>>
>>
>>     -thomas
>>
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>