R -显示多个地图，但绘制的第二个取代了第一个

Question

library(ggplot2)
library(gridExtra)
date_start <- seq(as.Date("2015-01-01"), by = "1 day", length.out = 30)
date_end   <- seq(as.Date("2015-01-02"), by = "1 day", length.out = 30)
date <- data.frame(date_start = date_start,
                   date_end   = date_end)
date <- date[1:3, ] # to make this example shorter.
plots <- list()
for (i in 1:nrow(date)){
  json_string <- paste0("http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=",
                        date[i, 1],
                        "&endtime=",
                        date[i, 2],
                        "&minmagnitude=5")
  print(json_string)
  jsonData <- jsonlite::fromJSON(json_string)  
  magnitudes <- jsonData$features$properties$magi
  latitude   <- jsonData$features$geometry$coordinates[]
  long  <- (lapply(latitude,"[",1))
  long1 <- c(do.call("cbind",long)) 
  lat   <- lapply(latitude,"[",2)
  lat1  <- c(do.call("cbind",lat))  
  mp <- NULL 
  mapWorld <- borders("world", colour="gray50", fill="gray50")
  mp <- ggplot() + mapWorld 
  plots[[i]] <- mp + geom_point(aes(x=long1, y=lat1,size = (magnitudes)) ,color="blue")
}
grid.arrange(plots[[1]],plots[[2]], ncol = 1, main = "Earthquakes")

问题是，2张地图是按照计划创建的，但第二张地图的情节都取代了第一张地图。这发生在循环运行的第二次。我也试过[[1,exact=TRUE]]，但都没有效果。

而第一个单独显示的图显示了所需的输出。如果在循环中第二次绘制，输出将被覆盖。

谁来帮帮我。被困了好几天

Answer 1

您将想要创建数据帧并在geom_point中显式调用它-以下内容应该正确工作:

for (i in 1:nrow(date)){
  json_string <- paste0("http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=",
                        date[i, 1],
                        "&endtime=",
                        date[i, 2],
                        "&minmagnitude=5")
  print(json_string)
  jsonData <- jsonlite::fromJSON(json_string)  
  magnitudes <- jsonData$features$properties$magi
  coords     <- jsonData$features$geometry$coordinates[]
  long1 <- sapply(coords, "[", 1)
  lat1  <- sapply(coords, "[", 2)
  df <- data.frame(long1 = long1,
                   lat1  = lat1)
  mp <- NULL 
  mapWorld <- borders("world", colour="gray50", fill="gray50")
  mp <- ggplot() + mapWorld 
  plots[[i]] <- mp + 
    geom_point(data = df, aes(x = long1, y = lat1, size = (magnitudes)), color = "blue") +
    ggtitle(paste0("iteration: ", i))
}