我正在尝试理解import UIKit
postfix operator %
postfix func % (percentage: Int) -> Double {
return (Double(percentage) / 100)
}
class ViewController: UIViewController {
var percentage = Double()
override func viewDidLoad() {
super.viewDidLoad()
percentage = 25%
print(percentage)
}
}
中非等同连接的结果如何在data.table - 变量的每个级别中在中排序的基础逻辑。
从头开始说清楚：我对订单本身没有任何问题，或者在加入后以所需的方式订购输出。但是，因为我发现所有其他on操作的输出高度一致，我怀疑在非equi连接中也有一个排序模式。
我将举两个例子，其中两个不同的“大”数据集以较小的方式连接。我试图在每个连接的输出中描述最明显的模式，以及模式在两个数据集的连接之间的实例。
data.table第一个大数据集与小library(data.table)
# the first 'large' data set
d1 <- data.table(x = c(rep(c("b", "a", "c"), each = 3), c("a", "b")),
y = c(rep(c(1, 3, 6), 3), 6, 6),
id = 1:11) # to make it easier to track the original order in the output
# x y id
# 1: b 1 1
# 2: b 3 2
# 3: b 6 3
# 4: a 1 4
# 5: a 3 5
# 6: a 6 6
# 7: c 1 7
# 8: c 3 8
# 9: c 6 9
# 10: a 6 10
# 11: b 6 11
# the small data set
d2 <- data.table(id = 1:2, val = c(4, 2))
# id val
# 1: 1 4
# 2: 2 2
之间的非等连接。
on = .(y >= val)第二个“大”数据集：
d1[d2, on = .(y >= val)]
# x y id i.id
# 1: b 4 3 1 # Row 1-5, first match: y >= val[1]; y >= 4
# 2: a 4 6 1 # The rows within this match have the same order as the original data
# 3: c 4 9 1 # and runs consecutively from first to last match
# 4: a 4 10 1
# 5: b 4 11 1
# 6: b 2 2 2 # Row 6-13, second match: y >= val[2]; y >= 2
# 7: a 2 5 2 # The rows within this match do not have the same order as the original data
# 8: c 2 8 2 # Rather, they seem to be come in chunks (6-8, 9-11, 12-13)
# First chunk starts with the match with lowest index, y[2]
# 9: b 2 3 2
# 10: a 2 6 2
# 11: c 2 9 2
# 12: a 2 10 2
# 13: b 2 11 2
第二个大数据集与小：
之间的非等连接d3 <- data.table(x = rep(c("a", "b", "c"), each = 3),
y = c(6, 1, 3),
id = 1:9)
# x y id
# 1: a 6 1
# 2: a 1 2
# 3: a 3 3
# 4: b 6 4
# 5: b 1 5
# 6: b 3 6
# 7: c 6 7
# 8: c 1 8
# 9: c 3 9
任何人都可以解释（1）在d3[d2, on = .(y >= val)]
# x y id i.id
# 1: a 4 1 1 # Row 1-3, first match (y >= 4), similar to output above
# 2: b 4 4 1
# 3: c 4 7 1
# 4: a 2 3 2 # Row 4-9, second match (y >= 2).
# 5: b 2 6 2 # Again, rows not consecutive.
# 6: c 2 9 2 # However, now the first chunk does not start with the match with lowest index,
# y[3] instead of y[1]
# 7: a 2 1 2 # y[1] appears after y[3]
# 8: b 2 4 2 # ditto
# 9: c 2 7 2
变量的每个级别中的顺序的逻辑，特别是在 second 匹配中，其中原始数据的顺序不保留在结果中。 （2）当使用两个不同的数据集时，为什么块中的