r - “进程已分叉......”在 R 中使用 tm 包时出错

Question

我安装了tm packageinR来做一些文本挖掘分析。创建语料库后，我想使用该tm_map()函数，该函数会引发以下错误消息：

The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().Break on 

有人知道为什么会出现此消息吗？

这是更多用于说明的代码：

> require(tm)
Lade nötiges Paket: tm
> a <-Corpus(VectorSource(chi2014_df$text))
> a
A corpus with 70 text documents
> a <-tm_map(a,tolower)
The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().
Break on 

我在 OSX 10.7.5 上使用 R 3.0.1 GUI 1.61 Snow Leopard build (6492)

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