gistfile1.txt

# load reshape2 package
library(reshape2)
# reshape gdp_per_capita data frame
gdp_per_capita <- melt(gdp_per_capita, id.vars="Country", variable.name = "Years", value.name="GDP per capita", na.rm = TRUE)
str(gdp_per_capita)

## 'data.frame':    43252 obs. of  3 variables:
##  $ Country       : chr  "Afghanistan" "Albania" "Algeria" "Andorra" ...
##  $ Years         : Factor w/ 214 levels "1800","1801",..: 1 1 1 1 1 1 1 1 1 1 ...
##  $ GDP per capita: num  634 861 1360 1260 650 ...

# change factor to numeric
gdp_per_capita$Years <- as.numeric(as.character(gdp_per_capita$Years))
str(gdp_per_capita)

## 'data.frame':    43252 obs. of  3 variables:
##  $ Country       : chr  "Afghanistan" "Albania" "Algeria" "Andorra" ...
##  $ Years         : num  1800 1800 1800 1800 1800 1800 1800 1800 1800 1800 ...
##  $ GDP per capita: num  634 861 1360 1260 650 ...

head(gdp_per_capita)
##                Country Years GDP per capita
## 2          Afghanistan  1800       634.4000
## 4              Albania  1800       860.5880
## 5              Algeria  1800      1360.0000
## 7              Andorra  1800      1260.0000
## 8               Angola  1800       650.0000
## 10 Antigua and Barbuda  1800       796.5934