未记录的 SAS 过程步

前阵子，有一位网友提及 SAS 中有 monotonic() 这么一个未记录在软件手册中的函数1。其实除了函数之外，SAS 中有更多的未记录过程步。比如早期的实现多线程排序的 proc sortt、用来检查单词拼写的 proc spell、用编程的方式编辑数据集中数据的 proc editor、用编程的方式编辑 DMS 环境的工具条的 proc toolbar 等等。这些过程步的相关说明已经消失在了软件手册中，你仅能在网络上找到零星的记录，但如果你尝试提交相关的命令，你会发现它们仍然可用。

关于这些未记录的过程步，Paul Kent (1984年加入SAS) 曾对其中一种可能做出过解释2：

At times we've issued "the same proc with a new name" as a way of allowing us to get feedback on extensions to that procedure, without completely putting everyones production workload at risk. In the past we've seen TREPORT - new features in proc report; TFREQ - new statistics in proc freq, and SORTT - the threaded implementation... Sometimes we can prototype new features simply with new options in the existing PROC. It's usually a judgement call related to how invasive the new feature is to the structure of the production code.

We want power users to kick the tyres (for my UK friends) on some new features or implementation before they become permanent... So they remain undocumented (mostly) because the features are "transient" in the sense that they migrate into the "official" versions of the procedures, or they were not such good ideas to start with. And they remain implemented (mostly) so as not to overly in-convenience any early adopters who have been so bold as to use them in production jobs... Hope that helps y'all understand our motivation (at least a little bit)

另外有一种可能，就是随着时代的发展，某些功能已经"无用武之地"，例如 proc explode3。

在查找资料时，我还发现一个特别的例子——proc delete，它很早就被设计出来，但从 SAS 6 开始消失在了软件手册中，而从 SAS 9.4 开始又出现在了软件手册中，你可以通过查询早期的软件手册来确认这一点。它的这种行为可能是为 proc datasets 中的 delete 语句让位，但又有过多人坚持使用它，也可能是相关功能进行了回炉重造4。时间久远，佐证难查，小小的变迁大概已经成了时代的浪花。

参考：
[1] http://www.datascientist-club.cn/forumDetail/584

[2] http://www.notecolon.info/2010/10/what-is-proc-sortt.html

[3] https://communities.sas.com/t5/SAS-Communities-Library/PROC-EXPLODE-The-SAS-procedure-that-time-forgot/ta-p/473102

[4] https://blogs.sas.com/content/sasdummy/2013/07/08/proc-delete-its-not-dead-yet/