Looping over variables to generate interaction variables-CodePudding

For each variable in var1, I want its interaction with each variable in var2. In Stata, I can simply use a nested foreach loop to do this but I am not able to replicate the logic in R.

Stata code:

foreach var1 in
    gdp_g gdp_g_l GPCP_g GPCP_g_l
{;
foreach var2 in
    polity2l y_0 ethfrac Oil lmtnest 
{;
quietly gen `var1'_`var2' = `var1'*`var2';
};
};

Not sure about the intuition in R.

vars1 <- list("gdp_g", "gdp_g_l", "GPCP_g", "GPCP_g_l")
vars2 <- list("polity2l", "y_0", "ethfrac", "Oil", "lmtnest")

multiplyit <- function(x){
  paste(x, collapse = "*")
}

for(i in 1:length(vars1)) {
  for(j in 1:length(var2)){
    vars1[i]*vars2[j]
  }
}

Maybe I need to use a formula to multiply each unique combination of variables.

CodePudding user response：

You can use combn from combinat package to get all unique combination of pairs, then collapse all strings separated by * using paste

> library(combinat)
> combn(c(vars1, vars2), 2, fun = paste, collapse="*")
 [1] "gdp_g*gdp_g_l"     "gdp_g*GPCP_g"      "gdp_g*GPCP_g_l"    "gdp_g*polity2l"    "gdp_g*y_0"        
 [6] "gdp_g*ethfrac"     "gdp_g*Oil"         "gdp_g*lmtnest"     "gdp_g_l*GPCP_g"    "gdp_g_l*GPCP_g_l" 
[11] "gdp_g_l*polity2l"  "gdp_g_l*y_0"       "gdp_g_l*ethfrac"   "gdp_g_l*Oil"       "gdp_g_l*lmtnest"  
[16] "GPCP_g*GPCP_g_l"   "GPCP_g*polity2l"   "GPCP_g*y_0"        "GPCP_g*ethfrac"    "GPCP_g*Oil"       
[21] "GPCP_g*lmtnest"    "GPCP_g_l*polity2l" "GPCP_g_l*y_0"      "GPCP_g_l*ethfrac"  "GPCP_g_l*Oil"     
[26] "GPCP_g_l*lmtnest"  "polity2l*y_0"      "polity2l*ethfrac"  "polity2l*Oil"      "polity2l*lmtnest" 
[31] "y_0*ethfrac"       "y_0*Oil"           "y_0*lmtnest"       "ethfrac*Oil"       "ethfrac*lmtnest"  
[36] "Oil*lmtnest"

CodePudding user response：

You can take a tidyverse approach as follows.

library(tidyverse)

map(vars1, ~ str_c(., vars2, sep = "*")) %>% 
  unlist()

# [1] "gdp_g*polity2l"    "gdp_g*y_0"         "gdp_g*ethfrac"     "gdp_g*Oil"         "gdp_g*lmtnest"    
# [6] "gdp_g_l*polity2l"  "gdp_g_l*y_0"       "gdp_g_l*ethfrac"   "gdp_g_l*Oil"       "gdp_g_l*lmtnest"  
# [11] "GPCP_g*polity2l"   "GPCP_g*y_0"        "GPCP_g*ethfrac"    "GPCP_g*Oil"        "GPCP_g*lmtnest"   
# [16] "GPCP_g_l*polity2l" "GPCP_g_l*y_0"      "GPCP_g_l*ethfrac"  "GPCP_g_l*Oil"      "GPCP_g_l*lmtnest"