GH中数据选取的语法规则变更（DataTree selection rules）

今天在处理一组树状数据结构的时候用到split tree这个电池，发现原先的masks的语法规则发生了变化，之前例如我需要提取前6个branches，需要写0-6即可，但是今天一直出错，上网一搜才发现在0.9版本后数据选取的规则发生了变化，现在需要写成0 to 6。为了方便大家之后在其他地方产生疑惑的查询，将作者David Rutten解释帖引用并提供链接，很简单的内容就不翻译了哈。顺带说一句，其实基本上对于树状结构的处理都可以通过Param Viewer转换成List的问题再用Tree Branch转回，但是既然都有这些直接处理树状结构的命令，还是应该多多挖掘其中的强大，例如下面内容会提到的类似编程语言的？和！的用法，会在某些时候给你带来意想不到的便捷。（单位没法上传图片就没法一一截图了，大家探索愉快！）
From David Rutten：

Imagine we have the following data tree, containing a bunch of textual characters:

[size=1em]{0;0} = [a,e,i,o,u,y]
{0;1} = [ä,ë,ê,ï,î,ö,ô,õ,ü,û,ÿ,y]
{1;0} = [b,c,d,f,g,h,j,k,l,m,n,p,q,r,s,t,v,w,x,z]
{1;1} = [ç,ĉ,č,ĝ,ř,š,ş,ž]

There are a total of four branches {0;0}, {0;1}, {1;0} and {1;1}. The first branch contains all the vowels that are part of the standard English alphabet. The second branch contains all non-standard vowels and branches three and four contain the standard and non-standard consonants respectively.

So what if we want to select from this tree only the standard vowels? Basically include everything in the first branch and disregard everything else. We can use the [Tree Split] component with a selection rule to achieve this:

[size=1em]{0;0}

This selection rule hard-codes the number zero in both tree path locations. It doesn't define an item index rule, so all items in {0;0} will be selected.

If we want all the vowels (both standard and non-standard), then we have several options:

[size=1em]{0;?}         = select all branches that start with 0

[size=1em]{0;(0,1)}    = select all branches that start with 0 and end in either 0 or 1

[size=1em]{0;(0 to 1)} =    ......................................... and end in the range 0 to 1.

Conversely, selecting all standard vowels and consonants while disregarding all non-standard character can be achieved with rules as follows:

[size=1em]{?;0}

[size=1em]{(0,1);0}

[size=1em]{(0 to 1);0}

It is also possible to select items from each branch in addition to limiting the selection to specific branches. In this case another rule stated in square brackets needs to be appended:

[size=1em]{0;?}[0 to 2]

The above rule will select the first three vowels from the standard and the non-standard lists.

Basically, rules work in a very consistent way, but there are some syntax conventions you need to know. The first thing to realize is that every individual piece of data in a data-tree can be uniquely and unambiguously identified by a collection of integers. One integer describes its index within the branch and the others are used to identify the branch within the tree. As a result a rule for selection items always looks the same:

[size=1em]{A;B;C;...;Z}              where A, B, C, Z and i represent rules.

It's very similar to the Path Mapper syntax except it uses square brackets instead of parenthesis for the index (the Path Mapper will follow suit soon, but that won't be a breaking change). You always have to define the path selector rule in between curly brackets. You can supply any number of rules as long as you separate them with semi-colons.

The index rule is optional, but -when provided- it has to be encased in square brackets after the path selection rule(s).

The following rule notations are allowed:

[size=1em]*  Any number of integers in a path

[size=1em]?  Any single integer

[size=1em]6  Any specific integer

[size=1em]!6  Anything except a specific integer

[size=1em](2,6,7)  Any one of the specific integers in this group.

[size=1em]!(2,6,7)  Anything except one of the integers in this group.

[size=1em](2 to 20)  Any integer in this range (including both 2 and 20).

[size=1em]!(2 to 20) Any integer outside this range.

[size=1em](0,2,...)  Any integer part of this infinite sequence. Sequences have to be at least two integers long, and every subsequent integer has to be bigger than the previous one (sorry, that may be a temporary limitation, don't know yet).

[size=1em](0,2,...,48)  Any integer part of this finite sequence. You can optionally provide a single sequence limit after the three dots.

[size=1em]!(3,5,...)  Any integer not part of this infinite sequence. The sequence doesn't extend to the left, only towards the right. So this rule would select the numbers 0, 1, 2, 4, 6, 8, 10, 12 and all remaining even numbers.

[size=1em]!(7,10,21,...,425)  Any integer not part of this finite sequence.

Furthermore, it is possible to combine two or more rules using the boolean and/or operators. If you want to select the first five items in every list of a datatree and also the items 7, 12 and 42, then the selection rule would look as follows:

[size=1em]{*}[(0 to 4) or (6,11,41)]

The asterisk allows you to include all branches, no matter what their paths looks like.

It is at present not possible to use the parenthesis to define rule precedence, rules are always evaluated from left to right. It is at present also not possible to use negative integers to identify items from the end of a list.

原始链接http://www.grasshopper3d.com/for ... ree-selection-rules

相关的变更还有表达式的写法