并非所有值都存储在循环中

Question

我想在 "yy" 中存储值，但我下面的代码只存储一行（最后一个值）。请查看下面的输出。有人可以帮助将所有值存储在 "yy"

中吗

提前致谢。我是 R 的初学者。

arrPol <- as.matrix(unique(TN_97_Lau_Cot[,6]))
arrYear <- as.matrix(unique(TN_97_Lau_Cot[,1]))

for (ij in length(arrPol)){
    for (ik in length(arrYear)) {
     newPolicy <- subset(TN_97_Lau_Cot, POLICY == as.character(arrPol[ij]) & as.numeric(arrYear[ik]))
     yy <- newPolicy[which.min(newPolicy$min_dist),]
  }
}

输出：

YEAR DIVISION STATE COUNTY CROP POLICY STATE_ABB LRPP min_dist
1: 2016        8    41     97   21 699609        TN    0      2.6

这是 "TN_97_Lau_Cot" 矩阵的图像。

Answer 1

不需要循环。可能是一种更简单的方法，但是两个基于集合的步骤比两个循环更好。这些是我会尝试的两种方法：

基础

# Perform an aggregate and merge it to your data.frame.
TN_97_Lau_Cot_Agg <- merge(
  x = TN_97_Lau_Cot, 
  y = aggregate(min_dist ~ YEAR + POLICY, data = TN_97_Lau_Cot, min),
  by = c("YEAR","POLICY"),
  all.x = TRUE
)

# Subset the values that you want.
TN_97_Lau_Cot_Final <- unique(subset(TN_97_Lau_Cot_Agg, min_dist.x == min_dist.y))

data.table

library(data.table)

# Convert your data.frame to a data.table.
TN_97_Lau_Cot <- data.table(TN_97_Lau_Cot)

# Perform a "window" function that calculates the min value for each year without reducing the rows.
TN_97_Lau_Cot[, minDistAggregate:=min(min_dist), by = c("YEAR","POLICY")]

# Find the policy numbers that match the minimum distance for that year.
TN_97_Lau_Cot_Final <- unique(TN_97_Lau_Cot[min_dist==minDistAggregate, -10, with=FALSE])

并非所有值都存储在循环中

Not all values storing in a loop

store

r