list R：遍历列表
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R: loop through list
提问by teeglaze
I've come over this problem a few times by now, and this time I am eager to get an efficient solution. The underlying problem is that I want to loop through a list of variables with the pastefunction.
我已经多次遇到这个问题，这次我渴望得到一个有效的解决方案。潜在的问题是我想用paste函数遍历变量列表。
dat <- read.csv("some file", header=TRUE)
list.R <- c("IC","IG","DM","IM","IN","EN","RM")
for (RO in list.R){
paste("dat$",RO,"_I", sep="")[
paste("dat$",RO,"_I", sep="") ==
"Strongly disagree"] <- 1
}
I pasted the name of the variable together, but this gives me a string in block quotes. I've tried the following but nothing worked so far:
我将变量的名称粘贴在一起，但这给了我一个包含块引号的字符串。我已经尝试了以下但到目前为止没有任何效果：
eval(parse(text=paste("dat$",RO,"_I", sep="")))
or
或者
get(paste("dat$",RO,"_I", sep=""))
do you know how to solve this so that the loop works? I would very much appreciate your help :)
你知道如何解决这个问题以便循环工作吗？我非常感谢您的帮助:)
(I know in this case I could also use as.numeric(levels(dat$IC_I))[dat$IC_I]but the order of the levels is wrong)
（我知道在这种情况下我也可以使用as.numeric(levels(dat$IC_I))[dat$IC_I]但级别的顺序是错误的）
回答by josliber
You can do this with simple assignment operators -- there's no need for a loop (as is usually the case in R). First, I'll construct a sample data frame, with your variables stored as the character type instead of as factors:
您可以使用简单的赋值运算符来做到这一点——不需要循环（R 中通常是这种情况）。首先，我将构建一个示例数据框，将您的变量存储为字符类型而不是因子：
dat <- data.frame(id=1:2, ID_I=c("Agree", "Strongly Disagree"), IG_I=c("Strongly Disagree", "Agree"), stringsAsFactors=FALSE)
dat
# id ID_I IG_I
# 1 1 Agree Strongly Disagree
# 2 2 Strongly Disagree Agree
Now you can use column indexing to replace "Strongly Disagree" with 1:
现在您可以使用列索引将“强烈不同意”替换为 1：
cols <- c("ID_I", "IG_I")
dat[,cols][dat[,cols] == "Strongly Disagree"] <- 1
dat
# id ID_I IG_I
# 1 1 Agree 1
# 2 2 1 Agree
