英文:
kotlin: how to use the Intermediate collection when do stream operations
问题
x代表coordinates的map结果。我想在'all'步骤中使用它，如何做到这一点？
英文:
for example
val coordinates: Array<IntArray> = [[1, 2], [1, 3], [1, 4]]
coordinates
.map {it[0]}
.all {it == x[0]}
x means the map result of coordinates. I want use it in the 'all' step, how to do that?
答案1
得分: 1
你可以只写这个
coordinates
.map { it[0] }
.all { it == coordinates[0][0] }
或者如果你不想直接再次引用坐标，也许插入一个 `let` 像这样
coordinates
.map { it[0] }
.let { x -> x.all { it == x[0] } }
虽然对于你的特定用例，我可能只会这样做
coordinates
.all { it[0] == coordinates[0][0] }
英文:
You could just write this
coordinates
.map {it[0]}
.all {it == coordinates[0][0]}
Or if you don't want to directly refer to coordinates again, maybe insert a let like
coordinates
.map { it[0] }
.let { x -> x.all { it == x[0] } }
Although for your specific use case I probably would just do
coordinates
.all { it[0] == coordinates[0][0] }
答案2
得分: 1
如果我理解正确，你可以简单地声明一个名为 x 的 val 变量：
val x = coordinates.map { it[0] }
val result = x.all { it == x[0] }
或者，如果你想在一个表达式中完成，你可以使用作用域函数 run 或 let：
val result = coordinates.map { it[0] }.run {
all { it == this[0] }
}
或者：
val result = coordinates.map { it[0] }.let { x ->
x.all { it == x[0] }
}
不过，如果你只想检查整个列表是否具有完全相同的唯一值，我认为以下方式更可读：
val result = coordinates.map { it[0] }.distinct().size == 1
上述方法不像 all 那样进行短路处理。要进行短路处理，需要使用 Sequence：
val result = coordinates
.asSequence()
.map { it[0] }
.distinct().take(2).count() == 1
英文:
If I understand correctly, you can just declare a val called x:
val x = coordinates.map { it[0] }
val result = x.all { it == x[0] }
Or if you want to do it in one expression, you can use the scope function run or let:
val result = coordinates.map { it[0] }.run {
all { it == this[0] }
}
or:
val result = coordinates.map { it[0] }.let { x ->
x.all { it == x[0] }
}
Though, if you just want to check if the whole list has exactly one unique value, I think this is more readable:
val result = coordinates.map { it[0] }.distinct().size == 1
The above doesn't short-circuit like all. A shortcircuiting version would need Sequence:
val result = coordinates
.asSequence()
.map { it[0] }
.distinct().take(2).count() == 1
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