r - 粘贴是绘图数学表达式中的特殊参数吗？

Question

当提供plotmath时表达情节标题我认为 paste就像 paste 一样工作，但现在我不确定。这是 plotmath 的特殊参数吗？功能？在绘图数学中paste()行为类似于 paste0()和paste0直接引用，而sep paste() 的参数被忽略，但不在表达式中引用。怎么样paste()解释？请参阅下面的四个示例:

#  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plotmath中不是经典paste 。请参阅?plotmath :

paste(x, y, z) juxtapose x, y, and z

paste在plotmath的背景下没有sep论证。

并且在源代码中plotmath.c你可以看到paste被重新定义:

/*----------------------------------------------------------------------
*
* 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;
}

它稍后在文件中发送:

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，所以我可能是错的)