R macros to enable user defined input similar to %let in SAS

Question

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 &.

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")

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

and replace the code as

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

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.

I am looking for something similar in R however.

Maybe `file.choose()`, or use `metric – zx8754 Jul 14 '16 at 06:52 — zx8754, Jul 14 '16 at 06:52

score 2 · Accepted Answer · edited May 23 '17 at 12:08

2

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)

or wrapped in a function

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'))

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

Regarding to variable names you can do:

eval(parse(....)) will work

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

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

Full explanation in this SO Q/A

Hope it helps

edited May 23 '17 at 12:08

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answered Jul 14 '16 at 06:58

Altons

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The first solution is great. However I also wanted to know if this is possible for variables like say. Min_max_Ratio_smoothGNI – user36176 Jul 14 '16 at 07:18
how are you planning to use those variables? reporting? modelling? you can follow the same logic – Altons Jul 14 '16 at 07:28
I have expanded my answer to cover the 2nd part of your original question – Altons Jul 14 '16 at 07:36

R macros to enable user defined input similar to %let in SAS

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