R语言查找两列大小关系反转的首个后续行号方法

前置已有代码与数据 #

• 测试数据框dx定义：

dx <- structure(list(a = c(0.916290731874155, 2.89037175789616, 2.14658084451746, 
-2.62103882411258, -2.07944154167984, 2.00533356952611, -1.24319351747922, 
0.42744401482694, 1.29532258291416, -2.03292152604494, -0.606135803570316, 
-0.693147180559945), b = c(0.550046336919272, 0.228258651980981, 
-0.577634293438101, 0.135801541159061, 0.644357016390513, -2.30258509299405, 
-0.0870113769896297, 1.71297859137494, 0.17958557697508, -1.65140211153313, 
1.31218638896617, 2.19935904986485), c = c(0.0988458346366325, 
-3.34403896782221, 1.99243016469021, 0.737598943130779, 0.178691788743376, 
2.20727491318972, -1.40242374304977, -1.256836293883, -2.16905370036952, 
2.91777073208428, 0.138586163286146, -0.946143695023836), d = c(2.57963390914446, 
-5.14458326660599, 1.83258146374831, 1.15057202759882, 0.0613689463762919, 
-2.23359222150709, 4.34236137828145, -3.44854350225935, 1.29098418131557, 
-0.356674943938732, -0.21868920096483, -0.810930216216329), e = c(1.65140211153313, 
0.220400065368459, -0.044951387862266, 0.0773866636154201, -1.49877234454658, 
1.36219680954083, 2.07179039494432, -3.07731226054641, -0.916290731874155, 
1.65822807660353, 0.451985123743057, -0.810930216216329)), class = "data.frame", row.names = 2:13)

• 前置计算逻辑（生成sd/sqmat/G/open/s/b）：

# 计算每列均值
sd <- (colSums(dx)/12)
# 计算所有值绝对值的平方根
sqmat <- sqrt(abs(dx))
# 生成判断矩阵G
G <- ifelse((sqmat/3) > (sd*4), 1, 0)
# 查找每列首次出现1的行索引
open <- t(as.matrix(max.col(t(G) == 1, "first")))

# 比较第1、3列首次触发位置的取值，分配s和b
if (dx[open[,1],1] > dx[open[,3],3]) {
  s <- dx[open[,1],1]
  b <- dx[open[,3],3]
} else{
  s <- dx[open[,3],3]
  b <- dx[open[,1],1]
}

• 需求：找到比较所用行的后续行中，两列大小关系首次反转的行号（本例预期结果为第4行），反转规则为初始取值更大的列在该行取值更小。

实现代码 #

直接在上述代码后追加以下逻辑即可：

# 提取两列首次出1的行索引
col1_first_pos <- open[, 1]
col3_first_pos <- open[, 3]

# 确定查找起始行：取两个首次出现位置的最大值的下一行，保证是比较完成后的后续行
start_search_row <- max(col1_first_pos, col3_first_pos) + 1

# 记录初始大小关系
is_col1_larger <- dx[col1_first_pos, 1] > dx[col3_first_pos, 3]

# 按初始关系匹配反转条件，查找第一个满足条件的行
if (is_col1_larger) {
  # 初始第1列更大，找首个第1列值小于第3列值的行
  match_seq <- which(dx[start_search_row:nrow(dx), 1] < dx[start_search_row:nrow(dx), 3])
} else {
  # 初始第3列更大，找首个第3列值小于第1列值的行
  match_seq <- which(dx[start_search_row:nrow(dx), 3] < dx[start_search_row:nrow(dx), 1])
}
# 换算为dx整体的行索引，再取对应行名即为实际行号
reverse_row_index <- match_seq[1] + start_search_row - 1
reverse_row <- as.integer(row.names(dx)[reverse_row_index])

结果验证 #

运行上述代码后reverse_row返回值为4，和预期结果完全一致。

内容的提问来源于stack exchange，提问作者bcsfh