如何使用 Rebol 在块内创建子块

Question

我想得到

[["1" "a"] ["2" "b"]]

来自

["1" "" "a" "2" "" "b"]

什么是正确且最优雅的方式？我试过了，但没有得到我想要的结果：

block: ["1" "" "a" "2" "" "b"]

new-block: []
sub-block: []

foreach [first second third] block [
  sub-block: []
  append sub-block first
  append sub-block third
  append new-block sub-block
]

Answer 1

newblock: copy [] forskip block 3 [repend/only newblock [block/1 block/3 ]]
== [["1" "a"] ["2" "b"]]

Answer 2

foreach [a b c] block [repend/only [] [a c]]

Answer 3

另一种方法是使用 COLLECT/KEEP:

collect [
    foreach [first second third] block [
        keep/only collect [
            keep first
            keep third
        ]
    ]
]

Answer 4

另一种不太优雅的方法是：

>> parse ["1" "" "a" "2" "" "b"] [
         2 [set a string! skip set b string!
            (append x: [] reduce [a b])
         ]
   ]
>> x
== ["1" "a" "2" "b"]

Answer 5

为了更多样化，这里有一个使用 MAP-EACH

的解决方案

map-each [first second third] block [reduce [first third]]

注意。以上在 Rebol (2 & 3) 中有效。 MAP-EACH 目前没有红色版本。

如何使用 Rebol 在块内创建子块

How to create subblock inside block with Rebol

rebol