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在为情节标题提供plotmath表达式时，我认为它的paste工作方式就像paste，但现在我不确定。它是函数的特殊参数plotmath吗？在 plotmath 中的paste()行为类似于paste0()并被paste0直接引用，而 的sep参数paste()被忽略，但未在表达式中引用。是如何paste()解释的？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 )

在此处输入图像描述

4

1 回答 1

6

的确paste在plotmath中不是经典paste。见?plotmath：

paste(x, y, z) 并列 x、y 和 z

paste在plotmath没有sep论据的情况下。

在源代码中plotmath.c你可以看到它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;
}

它稍后在文件中分派：

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）

于 2013-10-24T14:52:10.220 回答