在plotmath表达式中粘贴一个特殊参数？

Question

在为plotmath情节标题提供表达时,我觉得它的paste效果就像paste,但现在我不确定.它是plotmath函数的特殊参数吗？在plotmath paste()行为就像paste0()和paste0被直接引用,而sep的论点paste()被忽略,但在表达没有报价.怎么paste()解释？请参阅以下四个示例:

#  Data to plot
x <- seq( 55 , 70 , length = 2001 )
probs <- dexp( x , rate = 5 / 60  )
s <- sample( x , 10000 , prob = probs , repl = TRUE )


#  Some plots
par(mfrow = c(2,2) )
#1)  paste() behaves like paste0() here
hist( s , breaks = 30 , 
    main = expression( paste( "1: Sampling of" , Phi , "Distribution" ) ) ,
    xlab = "No spaces in title using paste()" , axes = F )

#2)  add spaces in the expression where they are needed
hist( s , breaks = 30 , 
    main = expression( paste( "2: Sampling of "  , Phi , " Distribution" ) ) ,
    xlab = "Single spaces in titles: paste() behaves like paste0()" , axes = F )

#3)  Don't put spaces, use a sep argument - ignored
hist( s , breaks = 30 , 
    main = expression( paste( "3: Sampling of"  , Phi , "Distribution" , sep = " " ) ) ,
    xlab = "No spaces using paste(), `sep` argument is ignored but not quoted in expression" , axes = F )

#4)  paste0 is not recognised
hist( s , breaks = 30 , 
    main = expression( paste0( "4: Sampling of " , Phi , " Distribution" ) ) ,
    xlab = "paste0() not recognised" , axes = F )

Answer 1

确实paste在情节上不是经典paste。见?plotmath：

paste（x，y，z）将x，y和z并置

paste在plotmath没有sep参数的情况下。

在源代码中，plotmath.c您可以看到它paste已重新定义：

/*----------------------------------------------------------------------
*
* Code for Concatenate Expressions
*
*/

static int ConcatenateAtom(SEXP expr)
{
    return NameAtom(expr) && NameMatch(expr, "paste");
}

static BBOX RenderConcatenate(SEXP expr, int draw, mathContext *mc,
                         pGEcontext gc, pGEDevDesc dd)
{
    BBOX bbox = NullBBox();
    int i, n;

    expr = CDR(expr);
    n = length(expr);

    for (i = 0; i < n; i++) {
        bbox = CombineBBoxes(bbox, RenderElement(CAR(expr), draw, mc, gc, dd));
        if (i != n - 1)
         bbox = RenderItalicCorr(bbox, draw, mc, gc, dd);
        expr = CDR(expr);
    }
    return bbox;
}

稍后在文件中调度：

static BBOX RenderFormula(SEXP expr, int draw, mathContext *mc,
                         pGEcontext gc, pGEDevDesc dd)
{
    SEXP head = CAR(expr);

    ....
    else if (ConcatenateAtom(head))
        return RenderConcatenate(expr, draw, mc, gc, dd);
    ....

（话虽这么说，我对C一无所知，所以我可能错了）