r-在data.frame中获取用户指定变量的数据

Question

我昨天问了这个问题，得到了回答，但我认为他们并没有真正理解我的问题。我需要从数据库中提取数据。但是用户提供了变量列表。我需要我的代码循环遍历每个请求的变量，提取与之相关的数据，并将其放入data.frame中，以便进行分析。

f.extractVariables<-
  structure(function 
(dbPath,dbName,table,variables
   ){
# LOAD LIBRARIES
require(RODBC)
require(xlsx)
 setwd(dbPath)
 db <- odbcConnectAccess2007(dbName)
 #This was my idea on how to loop through the variable list but it won't run
 for (i in 1:length(variables))
  {
 dataCollection <- sqlQuery(db, 'SELECT table.variables[[i]]
                    FROM table;')
 }
#This piece was the solution I was given which runs but all it does is parrot back 
#the variable list it doesn't retrieve anything.
 variables=paste(variables,collapse=",")
 query<-paste(paste("SELECT",variables),
 "FROM table",sep='n')
 cat(query)
odbcClose(db)
 }
 )
#And the user provided input looks something like this. I can change the way the
 #variable list comes in to make it easier.
            dbPath = 'z:/sites/'
    dbName = 'oysterSites.accdb'
    table  = 'tblDataSiteOysterSamplingPlan'
    variables= 'nwLon,nwLat,neLon,neLat'
    f.extractVariables(dbPath,dbName,table,variables)

Answer 1

您认为您在用哪种语言进行编码？这不是.NET…

删除此

 for (i in 1:length(variables))
  {
 dataCollection <- sqlQuery(db, 'SELECT table.variables[[i]]
                    FROM table;')
 }

在循环的所有循环中，'SELECT table.variables[[i]] FROM table;'将始终是SAME，并随着而变化（至少我猜你想做什么）

 for (i in 1:length(variables))
  {
 dataCollection <- sqlQuery(db, paste0('SELECT table.variables[[', i, ']]
                    FROM table;'))
 }

你说以上不起作用。没有必要继续审查您的代码，修复上面的问题，然后返回