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在Kotlin中添加限制joinToString的条件

kotlin list android java

nhp · 技术社区 · 7 年前

val texts = listOf("It is a",
                "long established fact that a reader will be distracted,",
                "by the readable content of a page when looking at its layout.",
                "The point of using Lorem Ipsum is that it has a more-or-less normal",
                "distribution of letters, as opposed to using, making it look like readable English.",
                " Many desktop publishing packages and web page,",
                "editors now use Lorem Ipsum as their default model text, and a search,",
                "for \'lorem ipsum\' will uncover many web sites still in their infancy",
                "Various versions have evolved over the years", ...)

我想添加一个分隔符并限制结果的长度。

利用 joinToString 和 subString ,我可以达到这个效果。

texts.filter { it.isNotBlank() }
                .joinToString(separator = " ")
                .substring()

连接管柱 仅当迭代器到达所以它不需要做任何“连接”和之后。

我怎么能这么做?

2 回复 | 直到 7 年前

forpas 7 年前

首次使用 takeWhile 限制总长度,然后 join

fun main(args: Array<String>) {
    val texts = listOf("It is a",
            "long established fact that a reader will be distracted,",
            "by the readable content of a page when looking at its layout.",
            "The point of using Lorem Ipsum is that it has a more-or-less normal",
            "distribution of letters, as opposed to using, making it look like readable English.",
            " Many desktop publishing packages and web page,",
            "editors now use Lorem Ipsum as their default model text, and a search,",
            "for \'lorem ipsum\' will uncover many web sites still in their infancy",
            "Various versions have evolved over the years")

    val limit = 130
    var sum = 0
    val str = texts.takeWhile { sum += it.length + 1;  sum <= limit }.joinToString(" ")

    println(str)
    println(str.length)
}

将打印

It is a long established fact that a reader will be distracted, by the readable content of a page when looking at its layout.
125

Ruwanka De Silva 7 年前

使用 limit joinToString

val substring = texts.filter { it.isNotBlank() }
                .joinToString(separator = " ", limit = 10, truncated = "")
                .substring(0)

注 truncated 要避免的参数 ...

既然原来的答案在寻找 MAX_LENGTH 因为上面的最终字符串长度解决方案不起作用。理想的是 takeWhile 如公认的答案。但它需要依赖外部变量。如果可能的话,我宁愿使用函数方法,但似乎没有。所以基本上我们需要使用谓词减少操作,所以稍微修改了 reduce 行得通

public inline fun <S, T : S> Iterable<T>.reduceWithPredicate(operation: (acc: S, T) -> S, predicate: (S) -> Boolean): S {
        val iterator = this.iterator()
        if (!iterator.hasNext()) throw UnsupportedOperationException("Empty collection can't be reduced.")
        var accumulator: S = iterator.next()
        while (iterator.hasNext() && predicate(accumulator)) {
            accumulator = operation(accumulator, iterator.next())
        }
        return accumulator
    }

因为我们处理的是字符串连接,并试图限制其长度,所以我们必须使用 substring 花时间 花时间

val joinedString = texts.filter { it.isNotBlank() }
                .reduceWithPredicate({ s1, s2 -> "$s1 $s2" }, { it.length < 100 })
                .substring(100)
assertTrue { joinedString.length < 100 }