如何通过sapply替换for循环或应用从MySQL加载空间数据的函数

问题描述 投票:-2回答:1

我在R中加载来自MySQL的多边形数据。我编写了一个工作正常的函数。我希望用更快的东西替换我的凌乱循环(应用还是应用?)

这适用于AWS ubuntu服务器,运行MySQL服务器5.7和R编程

# INSTALLING AND LOADING NECESSARY PACKAGES
packages = c("RMySQL","rgeos");
for (package in packages) {
  if (package %in% installed.packages()[,"Package"] == FALSE) {
    install.packages(package);
  }
}

lapply(packages, require, character.only = TRUE)

options(rds = list(
  "host" = "avanse-instance.cqzqewynskco.us-east-2.rds.amazonaws.com",
  "port" = 3306,
  "user" = [user],
  "password" = [password]
))

LoadBuildings <- function() {
  # Connect to the MySQL database
  db <- dbConnect(MySQL(), dbname = "watsan", host = options()$rds$host, 
                  port = options()$rds$port, user = options()$rds$user, 
                  password = options()$rds$password)
  # Construct the fetching query
  query1 <- paste("SELECT ST_AsText(geom_building) FROM building where zone = 'Charrier_Vertieres_1';")
  query2 <- paste("SELECT * FROM building where zone = 'Charrier_Vertieres_1';")
  # Submit the fetch query and disconnect
  polyg <- dbGetQuery(db, query1)
  dt <- dbGetQuery(db, query2)
  dbDisconnect(db)

  spdf <- SpatialPolygonsDataFrame(readWKT(polyg[1, ]), dt[1, ], match.ID = FALSE)
  for (i in 2:nrow(polyg)){
    spdf <- rbind(spdf, SpatialPolygonsDataFrame(readWKT(polyg[i, ]), dt[i, ], match.ID = FALSE))
  }
  return(spdf)
}

有没有其他方法可以解决这个问题的建议,也许使用apply或tapply?谢谢,抱歉讨厌的代码

r
1个回答
0
投票

你的for循环不是任何缓慢的原因。它正在用rbind构建你的数据框架,这将减慢你的速度。请尝试使用它

spdf <- vector("list", nrow(polyg))
for (i in seq_along(spdf)){
  spdf[[i]] <- SpatialPolygonsDataFrame(readWKT(polyg[i, ]), dt[i, ], match.ID = FALSE)
}

spdf <- do.call("rbind", spdf)

或者,您可以使用下一段代码。但我会惊讶地发现性能差异很大。

spdf <- 
  lapply(seq_len(nrow(polyg)),
         function(i){
           SpatialPolygonsDataFrame(readWKT(polyg[i, ]), dt[i, ], match.ID = FALSE)
         })
spdf <- do.call("rbind", spdf)
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