R宏可启用类似于SAS中的％let的用户定义输入 [英] R macros to enable user defined input similar to %let in SAS

问题描述

我正在尝试使R中的特定过程自动化，在该过程中，代码基本上保持不变，但是导入的输入文件会更改-路径和大多数文件名都是相同的，只是一个单词发生了更改-某些变量名发生了更改. 我想进行用户定义的这些更改:非常类似于SAS中的％let.我可以在其中用&.

I am trying to automate a particular process in R, where essentially the code remains the same but the input files imported change- the path and most of the file name is the same only one word changes- and certain variable names change. I would like to make these changes user defined: much like %let in SAS. where i can call a value with &.

例如，如果我有此特定的导入代码:

For example if i have this particular import code:

Category_sales<- read.csv("C:/Projects/Consumption curves/UKPOV/excel files/MSP_product_CC_2009_salespercap.csv")

我只希望MSP一词根据用户的需要进行更改. 在SAS中，我将定义一个宏变量，例如％let metric = MSP

Where I would like only the word MSP to change depending on what the user wants. In SAS I would define a macrovariable like say %let metric=MSP

并将代码替换为

`C:/Projects/Consumption curves/UKPOV/excel files/&metric_product_CC_2009_salespercap.csv`

如果我有一个变量，请说 MaxGNI ，并且我只希望用户定义/替换GNI部​​件，如 Max& econvar ，在该位置我可以拥有 econvar 定义为％let econvar = GNI 或其他任何指标.

Also If I have a variable say MaxGNI and I would like only the GNI part to be user defined/replaced like Max&econvar where I could have econvar defined as %let econvar= GNI or any other metric.

但是我正在寻找R中类似的东西.

I am looking for something similar in R however.

推荐答案

您可以使用paste0函数来完成此任务.

You can accomplish this task using the paste0 function.

metric <- "MSP"
infile <- paste0("C:/Projects/Consumption curves/UKPOV/excel files/",metric,"_product_CC_2009_salespercap.csv")
Category_sales <- read.csv(infile)

或包装在函数中

readCSV <- function(var) {
       metric <- var
       infile <- paste0("C:/Projects/Consumption curves/UKPOV/excel files/",metric,"_product_CC_2009_salespercap.csv")
       return(infile)

}

Category_sales <- read.csv(readCSV('MSP'))

您可以对字符串中需要替换的所有位应用相同的逻辑.

You can apply the same logic to all the bits that need to be replaced in your string.

关于变量名称，您可以执行以下操作:

Regarding to variable names you can do:

eval(parse(....))将起作用

data1 <- data.frame(column1 = 1:10, column2 = letters[1:10])
txt <- "data1$column2"

> eval(parse(text = txt))
 [1] a b c d e f g h i j
Levels: a b c d e f g h i j

对于您的特殊情况，您可以用相同的paste0逻辑替换txt来构建变量名.

For your particular case you can replace txt with the same paste0 logic to build your variable names.

此SO Q/A中的完整说明

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