如何从矩阵中提取附近的位置？

Question

我在 R 中得到了一个包含以公里为单位的距离的矩阵：

structure(c(0, 0.299178017189202, 0.472092562775104, 31.0627244156583, 
68.5367247200762, 138.470931004348, 0.299178017189202, 0, 0.298855070662631, 
31.1130225293117, 68.70216465045, 138.511349341572, 0.472092562775104, 
0.298855070662631, 0, 31.41104035093, 68.9840966568129, 138.808325566886, 
31.0627244156583, 31.1130225293117, 31.41104035093, 0, 42.1218726943979, 
107.425908015876, 68.5367247200762, 68.70216465045, 68.9840966568129, 
42.1218726943979, 0, 82.3261005757895, 138.470931004348, 138.511349341572, 
138.808325566886, 107.425908015876, 82.3261005757895, 0), .Dim = c(6L, 
6L), .Dimnames = list(c("260100023-01", "260100023-05", "260100034-01", 
"260100034-02", "260100238-00", "260201036-00"), c("260100023-01", 
"260100023-05", "260100034-01", "260100034-02", "260100238-00", 
"260201036-00")))

ID 代表不同的位置。现在，我想创建一个列表，为每个 ID 显示 40 公里半径内的其他 ID。我想这样做的关键是“if”函数。但是我不知道如何在矩阵的每个单元格上逐行应用它。

Answer 1

您可以从单个列中提取元素，其中距离最多为 40，如下所示：

col <- data[1, ]
col[col < 40]
## 260100023-01 260100023-05 260100034-01 260100034-02 
##   0.0000000    0.2991780    0.4720926   31.0627244

如您所见，生成的矢量的名称恰好是 40 公里以内的位置的 ID。使用 names()，我们可以提取 ID：

names(col[col < 40])
## [1] "260100023-01" "260100023-05" "260100034-01" "260100034-02"

现在我们知道如何对单个列执行此操作，我们可以对所有列使用 apply() 到运行此函数

apply(data, 2, function(col) names(col[col > 40]))
## $`260100023-01`
## [1] "260100238-00" "260201036-00"
## 
## $`260100023-05`
## [1] "260100238-00" "260201036-00"
## 
## $`260100034-01`
## [1] "260100238-00" "260201036-00"
## 
## $`260100034-02`
## [1] "260100238-00" "260201036-00"
## 
## $`260100238-00`
## [1] "260100023-01" "260100023-05" "260100034-01" "260100034-02" "260201036-00"
## 
## $`260201036-00`
## [1] "260100023-01" "260100023-05" "260100034-01" "260100034-02" "260100238-00"

如何从矩阵中提取附近的位置？

How to extract close-by locations from a matrix?

r

if-statement

matrix

data-analysis