4

我想创建一个地图，显示两个变量之间的双变量空间相关性。这可以通过制作二元 Moran's I 空间相关性的 LISA 图或使用Lee (2001)提出的 L 指数来完成。

双变量 Moran's I 没有在spdep库中实现，但 L 索引是，所以这是我尝试使用 L 索引但没有成功的方法。一个显示基于莫兰的解决方案的答案我也将非常受欢迎！

正如您从下面可重现的示例中看到的那样，到目前为止，我已经设法计算了本地 L 索引。我想做的是估计伪 p 值并创建一个结果地图，就像我们在 LISA 空间集群中使用的那些地图一样，具有 high-high, high-low, ..., low-low。

在此示例中，目标是创建一个在黑人和白人人口之间具有双变量 Lisa 关联的地图。应在 中创建地图ggplot2，显示集群：

  • 黑人的高度存在和白人的高度存在
  • 黑人多，白人少
  • 黑人的低存在和白人的高存在
  • 低存在的黑人和低存在的白人

可重现的例子

library(UScensus2000tract)
library(ggplot2)
library(spdep)
library(sf)

# load data
  data("oregon.tract")

# plot Census Tract map
  plot(oregon.tract)


# Variables to use in the correlation: white and black population in each census track
  x <- scale(oregon.tract$white)
  y <- scale(oregon.tract$black)


# create  Queen contiguity matrix and Spatial weights matrix
  nb <- poly2nb(oregon.tract)
  lw <- nb2listw(nb)


# Lee index
  Lxy <-lee(x, y, lw, length(x), zero.policy=TRUE)

  # Lee’s L statistic (Global)
    Lxy[1]
    #> -0.1865688811


# 10k permutations to estimate pseudo p-values
  LMCxy <- lee.mc(x, y, nsim=10000, lw, zero.policy=TRUE, alternative="less")

# quik plot of local L
  Lxy[[2]] %>% density() %>% plot() # Lee’s local L statistic  (Local)
  LMCxy[[7]] %>% density() %>% lines(col="red") # plot values simulated 10k times 


# get confidence interval of 95% ( mean +- 2 standard deviations)
  two_sd_above <- mean(LMCxy[[7]]) + 2 * sd(LMCxy[[7]])
  two_sd_below <- mean(LMCxy[[7]]) - 2 * sd(LMCxy[[7]])


# convert spatial object to sf class for easier/faster use
  oregon_sf <- st_as_sf(oregon.tract)


# add L index values to map object
  oregon_sf$Lindex <- Lxy[[2]]

# identify significant local results  
  oregon_sf$sig <- if_else( oregon_sf$Lindex < 2*two_sd_below, 1, if_else( oregon_sf$Lindex > 2*two_sd_above, 1, 0))


# Map of Local L index but only the significant results
  ggplot() + geom_sf(data=oregon_sf, aes(fill=ifelse( sig==T, Lindex, NA)), color=NA)

在此处输入图像描述

4

3 回答 3

5

那这个呢？

我正在使用常规的 Moran's I 而不是您建议的 Lee Index。但我认为基本的推理几乎是一样的。

正如您在下面看到的那样——以这种方式产生的结果与来自 GeoDA 的结果非常相似

library(dplyr)
library(ggplot2)
library(sf)
library(spdep)
library(rgdal)
library(stringr)
library(UScensus2000tract)

#======================================================
# load data
data("oregon.tract")

# Variables to use in the correlation: white and black population in each census track
x <- oregon.tract$white
y <- oregon.tract$black

#======================================================
# Programming some functions

# Bivariate Moran's I
moran_I <- function(x, y = NULL, W){
        if(is.null(y)) y = x

        xp <- (x - mean(x, na.rm=T))/sd(x, na.rm=T)
        yp <- (y - mean(y, na.rm=T))/sd(y, na.rm=T)
        W[which(is.na(W))] <- 0
        n <- nrow(W)

        global <- (xp%*%W%*%yp)/(n - 1)
        local  <- (xp*W%*%yp)

        list(global = global, local  = as.numeric(local))
}


# Permutations for the Bivariate Moran's I
simula_moran <- function(x, y = NULL, W, nsims = 1000){

        if(is.null(y)) y = x

        n   = nrow(W)
        IDs = 1:n

        xp <- (x - mean(x, na.rm=T))/sd(x, na.rm=T)
        W[which(is.na(W))] <- 0

        global_sims = NULL
        local_sims  = matrix(NA, nrow = n, ncol=nsims)

        ID_sample = sample(IDs, size = n*nsims, replace = T)

        y_s = y[ID_sample]
        y_s = matrix(y_s, nrow = n, ncol = nsims)
        y_s <- (y_s - apply(y_s, 1, mean))/apply(y_s, 1, sd)

        global_sims  <- as.numeric( (xp%*%W%*%y_s)/(n - 1) )
        local_sims  <- (xp*W%*%y_s)

        list(global_sims = global_sims,
             local_sims  = local_sims)
}


#======================================================
# Adjacency Matrix (Queen)

nb <- poly2nb(oregon.tract)
lw <- nb2listw(nb, style = "B", zero.policy = T)
W  <- as(lw, "symmetricMatrix")
W  <- as.matrix(W/rowSums(W))
W[which(is.na(W))] <- 0

#======================================================
# Calculating the index and its simulated distribution
# for global and local values

m   <- moran_I(x, y, W)
m[[1]] # global value

m_i <- m[[2]]  # local values

local_sims <- simula_moran(x, y, W)$local_sims

# Identifying the significant values 
alpha <- .05  # for a 95% confidence interval
probs <- c(alpha/2, 1-alpha/2)
intervals <- t( apply(local_sims, 1, function(x) quantile(x, probs=probs)))
sig        <- ( m_i < intervals[,1] )  | ( m_i > intervals[,2] )

#======================================================
# Preparing for plotting

oregon.tract     <- st_as_sf(oregon.tract)
oregon.tract$sig <- sig


# Identifying the LISA patterns
xp <- (x-mean(x))/sd(x)
yp <- (y-mean(y))/sd(y)

patterns <- as.character( interaction(xp > 0, W%*%yp > 0) ) 
patterns <- patterns %>% 
        str_replace_all("TRUE","High") %>% 
        str_replace_all("FALSE","Low")
patterns[oregon.tract$sig==0] <- "Not significant"
oregon.tract$patterns <- patterns


# Plotting
ggplot() + geom_sf(data=oregon.tract, aes(fill=patterns), color="NA") +
        scale_fill_manual(values = c("red", "pink", "light blue", "dark blue", "grey95")) + 
        theme_minimal()

通过更改置信区间（例如，使用 90% 而不是 95%），您可以获得与 GeoDa 更接近（但不完全相同）的结果。

我想剩余的差异来自于计算 Moran's I 的一种稍微不同的方法。我的版本给出了与moranpackage 中可用的函数相同的值spdep。但 GeoDa 可能使用了另一种方法。

地理数据分析 在此处输入图像描述

于 2017-07-23T14:53:38.663 回答
0

我想现在添加到线程中已经很晚了，但是 Lee 的 L 与您在这里所做的完全不同，这是 Wartenberg (1985) 的创新。这有一些潜在的缺点。主要是，它测试了x和y 的滞后之间的关系，正如@RogerioJB 通过解释空间滞后 y 是通过将模拟的 y 乘以邻接矩阵来计算的。Lee (2001) 的创新完全不同，它涉及 Pearson 的 r 和空间平滑标量 (SSS) 的集成，而是比较x和y之间的过程，而不是 y的滞后. @RogerioJB 采用的方法可以通过从 lee.mc 函数生成可能的本地 l 的分布来复制。反过来，结果可以以类似于 GeoDa 的高-高...低-低显着性聚类图的样式绘制。

于 2020-11-05T21:28:42.823 回答
0

根据@justin-k 的建议，我修改了@rogeriojb 的二元LISA 代码来计算Lee 的L 统计量。这种方法从spdep包创建一个修改过的lee.mc()函数来模拟本地 L 值。我在GitHub gist中提供了另一个带有点级数据的示例。

library(boot)
library(dplyr)
library(ggplot2)
library(sf)
library(spdep)
library(rgdal)
library(stringr)
library(UScensus2000tract)

#======================================================
# load data
data("oregon.tract")

# Variables to use in the correlation: white and black population in each census track
x <- oregon.tract$white
y <- oregon.tract$black

# ----------------------------------------------------- #
# Program a function
## Permutations for Lee's L statistic
## Modification of the lee.mc() function within the {spdep} package
## Saves 'localL' output instead of 'L' output
simula_lee <- function(x, y, listw, nsim = nsim, zero.policy = NULL, na.action = na.fail) {
  
  if (deparse(substitute(na.action)) == "na.pass") 
    stop ("na.pass not permitted")
  na.act <- attr(na.action(cbind(x, y)), "na.action")
  x[na.act] <- NA
  y[na.act] <- NA
  x <- na.action(x)
  y <- na.action(y)
  if (!is.null(na.act)) {
    subset <- !(1:length(listw$neighbours) %in% na.act)
    listw <- subset(listw, subset, zero.policy = zero.policy)
  }
  n <- length(listw$neighbours)
  if ((n != length(x)) | (n != length(y))) 
    stop ("objects of different length")
  gamres <- suppressWarnings(nsim > gamma(n + 1))
  if (gamres) 
    stop ("nsim too large for this number of observations")
  if (nsim < 1) 
    stop ("nsim too small")
  xy <- data.frame(x, y)
  S2 <- sum((unlist(lapply(listw$weights, sum)))^2)
  
  lee_boot <- function(var, i, ...) {
    return(lee(x = var[i, 1], y = var[i, 2], ...)$localL)
  }
  
  res <- boot(xy, statistic = lee_boot, R = nsim, sim = "permutation", 
              listw = listw, n = n, S2 = S2, zero.policy = zero.policy)
}

# ----------------------------------------------------- #
# Adjacency Matrix
nb <- poly2nb(oregon.tract)
lw <- nb2listw(nb, style = "B", zero.policy = T)
W  <- as(lw, "symmetricMatrix")
W  <- as.matrix(W / rowSums(W))
W[which(is.na(W))] <- 0

# ----------------------------------------------------- #
# Calculate the index and its simulated distribution
# for global and local values

# Global Lee's L
lee.test(x = x, y = y, listw = lw, zero.policy = TRUE,
         alternative = "two.sided", na.action = na.omit)

# Local Lee's L values
m <- lee(x = x, y = y, listw = lw, n = length(x), 
         zero.policy = TRUE, NAOK = TRUE)

# Local Lee's L simulations
local_sims <- simula_lee(x = x, y = y, listw = lw, nsim = 10000,
                         zero.policy = TRUE, na.action = na.omit)

m_i <- m[[2]]  # local values

# Identify the significant values 
alpha <- 0.05  # for a 95% confidence interval
probs <- c(alpha/2, 1-alpha/2)
intervals <- t(apply(t(local_sims[[2]]), 1, function(x) quantile(x, probs = probs)))
sig <- (m_i < intervals[ , 1] ) | ( m_i > intervals[ , 2])

#======================================================
# Preparing for plotting
oregon.tract <- st_as_sf(oregon.tract)
oregon.tract$sig <- sig

# Identifying the Lee's L patterns
xp <- scale(x)
yp <- scale(y)

patterns <- as.character(interaction(xp > 0, W%*%yp > 0)) 
patterns <- patterns %>% 
  str_replace_all("TRUE","High") %>% 
  str_replace_all("FALSE","Low")
patterns[oregon.tract$sig == 0] <- "Not significant"
oregon.tract$patterns <- patterns

# Plotting
ggplot() +
  geom_sf(data = oregon.tract, aes(fill = patterns), color = "NA") +
  scale_fill_manual(values = c("red", "pink", "light blue", "dark blue", "grey95")) + 
  guides(fill = guide_legend(title = "Lee's L clusters")) +
  theme_minimal()

用于 oregon.tract 数据的 Lee 的 L 聚类

于 2020-12-06T07:13:54.587 回答