R：使用“where”通过匹配列表中的元素来选择行答案

【问题标题】：R: use of "where" to select rows by matching an element from a listR：使用“where”通过匹配列表中的元素来选择行
【发布时间】：2012-03-28 14:45:29
【问题描述】：

我试图在循环中使用 R 中的“where”函数根据匹配元素从两个数据集中挑选出某一行，然后制作两者的散点图。他们下面的代码示例提供了两个数据框和循环的行名。每个数据框包含的县多于“mycounties”中列出的县。

我之前在循环中使用过“where”函数，但这次R返回了“where”不存在的错误消息？我知道“哪里”存在！我的问题是，如何让 R 识别这种“位置”结构，或者有没有更好的方法来挑选我想要绘制的行？

 > names(dts)
 [1] "county"  "Freq125" "Freq126" "Freq127" "Freq128" "Freq129" "Freq130" "Freq131" "Freq132" "Freq133" "Freq134" "Freq135" "Freq136" "Freq137"
[15] "Freq138" "Freq139" "Freq140" "Freq141" "Freq142" "Freq143" "Freq144" "Freq145" "Freq146" "Freq147" "Freq148" "Freq149" "Freq150" "Freq151"
[29] "Freq152" "Freq153" "Freq154" "Freq155" "Freq156" "Freq157" "Freq158" "Freq159" "Freq160" "Freq161" "Freq162" "Freq163" "Freq164" "Freq165"
[43] "Freq166" "Freq167" "Freq168" "Freq169" "Freq170" "Freq171"

> names(pm)
 [1] "county" "pm125m" "pm126m" "pm127m" "pm128m" "pm129m" "pm130m" "pm131m" "pm132m" "pm133m" "pm134m" "pm135m" "pm136m" "pm137m" "pm138m"
[16] "pm139m" "pm140m" "pm141m" "pm142m" "pm143m" "pm144m" "pm145m" "pm146m" "pm147m" "pm148m" "pm149m" "pm150m" "pm151m" "pm152m" "pm153m"
[31] "pm154m" "pm155m" "pm156m" "pm157m" "pm158m" "pm159m" "pm160m" "pm161m" "pm162m" "pm163m" "pm164m" "pm165m" "pm166m" "pm167m" "pm168m"
[46] "pm169m" "pm170m" "pm171m"
> 
> mycounties = c("beaufort", "bertie", "bladen", "camden", "carteret", "chowan", "craven", 
+   "cumberland", "currituck", "dare", "duplin", "gates", "greene", "harnett", "hyde",
+   "jones", "lenoir", "new hanover", "onslow", "pamlico", "pasquotank", "pender", "perquimans", "pitt", "robeson", "sampson", "tyrrell", "washington")
> 
> LOOP
> for (i in 1:length(mycounties)) {
+ x = pm[where(pm$county == mycounties[i]),2:48]
+ y = dt[where(dts$county == mycounties[i]),2:48 ]
+ plot( x, y, main=paste("HYSPLIT & ED Visits", counties[i], sep=""),
+  xlab="HYSPLIT", ylab="ED Visits", pch=19)
+ } 
Error in `[.data.frame`(pm, where(pm$county == mycounties[i]), 2:48) : 
  could not find function "where"

【问题讨论】：

标签： r loops plot where-clause

【解决方案1】：

就像 Jeff 和 cmets 所说，没有 where 函数。 which 是 R 版本。

但是，在此示例中，您根本不需要 which：

x <- pm[pm$county == mycounties[i], 2:48]
y <- dt[dt$county == mycounties[i], 2:48]

在你的例子中也是if 声明：

if (mat$county[i] %in% dt5$county)) {
    mat[i,2:58] = dt5[dt5$county == mat$county[i], 2:58]
}

假设您的dt5$county 与每个mat$county[i] 仅匹配一个县。否则会报错。

【讨论】：

【解决方案2】：

您是否尝试引用which() 函数？

【讨论】：

不，“在哪里”。这是我之前在类似循环中运行过的一行示例，效果很好： if (mat$county[i] %in% list(dt5$county)) {mat[i,2:58] = dt5[其中(mat$county[i] == dt5$county), 2:58]}
当您运行该行时，要么有人在别处定义了“where”函数，要么条件从未执行（即，(mat$county[i] %in% list(dt5$county)) 从未为真。where 肯定不是内置的在 R.which 中的函数是。
有趣！所以我之前使用的循环肯定产生了不正确的结果......我将不得不回去交叉检查它。谢谢！ Sooooo 在这种情况下可以使用“which”吗？我会试试？哪个
是的。看起来which 可以满足您的需求。我不熟悉where 函数。
事实上，我几乎可以肯定你给出的条件永远不会是真的。我假设mat 是一个矩阵，dt5 是一个数据框。在这种情况下，您的意思是使用mat$county[i] %in% dt5$county，而不是(mat$county[i] %in% list(dt5$county))，这绝不是真的。