life_expectancy = read.csv("life_expectancy.csv", skip = 2, header = TRUE, stringsAsFactors = FALSE)
sanitation = read.csv("sanitation.csv", skip = 2, header = TRUE, stringsAsFactors = FALSE)
 
## rename all yearly metric columns.  E.g., X1995 becomes le_1995 (for life expectancy)
names(life_expectancy)[grepl("\\bX", names(life_expectancy))] = gsub("X", "le_", names(le)[grepl("\\bX", names(life_expectancy))])
names(sanitation)[grepl("\\bX", names(sanitation))] = gsub("X", "san_", names(sanitation)[grepl("\\bX", names(sanitation))])
 
## lowercase column names
names(life_expectancy) = tolower(names(life_expectancy))
names(sanitation) = tolower(names(sanitation))