重新定义help_console函数以从给定的包获得函数的帮助

Question

下面是获得R函数帮助的函数。见下文：

help_console <-
function (topic, format = c("text", "html", "latex", "Rd"), lines = NULL,
    before = NULL, after = NULL)
{
    format = match.arg(format)
    if (!is.character(topic))
        topic <- deparse(substitute(topic))
    helpfile = utils:::.getHelpFile(help(topic))
    hs <- capture.output(switch(format, text = tools:::Rd2txt(helpfile),
        html = tools:::Rd2HTML(helpfile), latex = tools:::Rd2latex(helpfile),
        Rd = tools:::prepare_Rd(helpfile)))
    if (!is.null(lines))
        hs <- hs[lines]
    hs <- c(before, hs, after)
    cat(hs, sep = "\n")
    invisible(hs)
}

help_console(topic="lm", format = "text", lines=1)
Fitting Linear Models

现在，我想重新定义这个函数，以便从给定的包中获得关于R函数的帮助。这是我的MWE

help_console2 <-
function (topic, pkg, format = c("text", "html", "latex", "Rd"), lines = NULL,
    before = NULL, after = NULL)
{
    format = match.arg(format)
    if (!is.character(topic))
        topic <- deparse(substitute(topic))
    if (!is.character(pkg))
        topic <- deparse(substitute(pkg))
    helpfile = utils:::.getHelpFile(help(pkg, topic))
    hs <- capture.output(switch(format, text = tools:::Rd2txt(helpfile),
        html = tools:::Rd2HTML(helpfile), latex = tools:::Rd2latex(helpfile),
        Rd = tools:::prepare_Rd(helpfile)))
    if (!is.null(lines))
        hs <- hs[lines]
    hs <- c(before, hs, after)
    cat(hs, sep = "\n")
    invisible(hs)
}

help_console2(topic="lm", pkg="stats", format = "text", lines=1)

Error in find.package(if (is.null(package)) loadedNamespaces() else package,  : 
  there is no package called ‘topic’

这个函数是抛出错误。

Answer 1

您有错误的论证顺序，需要比非标准的评估更明智：

help_console2 <-
  function (topic, pkg, format = c("text", "html", "latex", "Rd"), lines = NULL,
            before = NULL, after = NULL)
  {
    format = match.arg(format)
    if (!is.character(topic))
      topic <- deparse(substitute(topic))
    if (!is.character(pkg))
      topic <- deparse(substitute(pkg))
    helpfile = utils:::.getHelpFile(do.call(help, list(topic=topic, package=pkg)))
    hs <- capture.output(switch(format, text = tools:::Rd2txt(helpfile),
                                html = tools:::Rd2HTML(helpfile), latex = tools:::Rd2latex(helpfile),
                                Rd = tools:::prepare_Rd(helpfile)))
    if (!is.null(lines))
      hs <- hs[lines]
    hs <- c(before, hs, after)
    cat(hs, sep = "\n")
    invisible(hs)
  }

help_console2(topic="lm", pkg="stats", format = "text", lines=1)
#Fitting Linear Models