[R] limited formula length in tsls

[Zsombor Cseres-Gergely]

Dear all,

Using the tsls package, I noticed that regression lists longer 
than 64 character
are getting truncated. Looking at the original source,

tsls.formula <- function(model, instruments, data, subset, weights,
    na.action, contrasts=NULL){
    if (missing(na.action)) 
        na.action <- options()$na.action
    m <- match.call(expand.dots = FALSE)
    if (is.matrix(eval(m$data, sys.frame(sys.parent())))) 
        m$data <- as.data.frame(data)
    m$formula <- model
    m$instruments <- m$model <- m$contrasts <- NULL
    m[[1]] <- as.name("model.frame")
    mf <- eval(m, sys.frame(sys.parent()))
    na.act <- attr(mf, "na.action")
    Z <- model.matrix(instruments, data, contrasts)
    response <- attr(attr(mf, "terms"), "response")
    y <- model.response(mf)
    X <- model.matrix(model, mf, contrasts)
    w <- model.weights(mf)
    if (missing(weights)) result <- tsls(y, X, Z, colnames(X))
    else result <- tsls.weighted(y, X, Z, w, colnames(X))
    result$formula <- model
    result$instruments <- instruments
    if (!is.null(na.act)) 
        result$na.action <- na.act
    class(result) <- "tsls"
    result
    }


I thought that the problem here is to handle the instruments correctly and
being consistent with the convention (?) regarding the single model object 
inside the function. Since I could not figure out, why the truncation occurs
(I tried as.character() and paste() in interactive mode, but nothing bad 
happened), I modified the source ad follows: 
   
 
tsls.formula <- function(model, instruments, data, subset, 
    na.action, contrasts=NULL){
    if (missing(na.action)) 
        na.action <- options()$na.action
    m <- match.call(expand.dots = FALSE)
    if (is.matrix(eval(m$data, sys.frame(sys.parent())))) 
        m$data <- as.data.frame(data)
    c1 <- as.character(model)
    c2 <- as.character(instruments)
    formula <- as.formula(paste(c1[2],c1[1],c1[3], '+', c2[2]))
    m$formula <- formula
    m$instruments <- m$model <- m$contrasts <- NULL
    m[[1]] <- as.name("model.frame")
    mf <- eval(m, sys.frame(sys.parent()))
    na.act <- attr(mf, "na.action")
    Z <- model.matrix(instruments, data = mf, contrasts)
    response <- attr(attr(mf, "terms"), "response")
    y <- mf[,response]
    X <- model.matrix(model, data=mf, contrasts)
    result <- tsls(y, X, Z, colnames(X))
    result$response.name <- c1[2]
    result$formula <- model
    result$instruments <- instruments
    if (!is.null(na.act)) 
        result$na.action <- na.act
    class(result) <- "tsls"
    result
    }

It works, but I feel that there is something wrong with it (although
it works fine so far). What?

Thank you,
Zsombor Cseres-Gergely 
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