using-rsv-api.Rnw

\documentclass[a4paper]{article}

\usepackage{listings}
\usepackage{inconsolata}

\usepackage[dvipsnames]{xcolor}

\usepackage[left=2.5cm,top=3cm,right=2.5cm,bottom=3cm,bindingoffset=0cm]{geometry}

\lstset{ %
  language=R,                     % the language of the code
  breakatwhitespace=false,        % sets if automatic breaks should only happen at whitespace
  keywordstyle=\color{NavyBlue},      % keyword style
  stringstyle=\color{JungleGreen},      % string literal style
  morekeywords={get_pxweb_data, TRUE}            % if you want to add more keywords to the set
} 


\title{Using the Icelandic Centre for Retail Studies PX-Web API}
\author{Palmar Thorsteinsson}

\begin{document}

\maketitle

<<echo=FALSE>>=
# Just for tidying display of code
  options(width=80)

  listing <- function(x, options) {
    paste("\\begin{lstlisting}[basicstyle=\\ttfamily,breaklines=true]\n",
      x, "\\end{lstlisting}\n", sep = "")
  }
  knit_hooks$set(source=listing, output=listing)
@

\section{Loading the PX-Web library}
Let's begin by loading the \texttt{pxweb} library that we will use for interacting with
the API. This ofcourse assumes that the library has been installed already.

<<main, echo=TRUE>>=
library(pxweb)
@

\section{Downloading individual series}
Next we download some data. Let's get the indices for sale of alcohol in fixed prices in 2015.

<<get_data, echo=TRUE>>=
url <- "http://px.rsv.is/PXWeb/api/v1/en/Sm%C3%A1s%C3%B6luv%C3%ADsitalan/Retail_turnover.px"

get_pxweb_data(url = url,
   dims = list(Year = c('14'),
               Month = c('*'),
               Prices = c('1'),
               Category = c('1'),
               "Indices and changes" = c('0')),
   clean = TRUE)
@

\newpage

\section{Downloading multiple series}
Finally we make a chart for each index. Let's begin by downloading the data.


<<get_indices_1, echo=TRUE>>=
url <- "http://px.rsv.is/PXWeb/api/v1/en/Sm%C3%A1s%C3%B6luv%C3%ADsitalan/Retail_turnover.px"
data <- get_pxweb_data(url = url,
               dims = list(Year = c('*'),
                           Month = c('*'),
                           Prices = c('1'),
                           Category = c('*'),
                           "Indices and changes" = c('0')),
               clean = TRUE)
@

\subsection{Creating proper timestamps}
In order to display the time series properly we must create a column in the data
set with a date value.

<<get_indices_2, echo=TRUE, warning=FALSE>>=
months <- data.frame(
  num = 1:12,
  name = month.name)
data <- merge(x=data, y=months, by.x="Month", by.y="name")
data$period <- as.Date(paste0(data$Year, "-", data$num, "-01"))
@

\subsection{Plotting the data}
Let's take a peek at the data before plotting.
<<get_indices_3, echo=TRUE, warning=FALSE>>=
head(data[,c(8,4,5,6)], n=10)
@

And finally plot all the series at once.

<<get_indices_4, echo=TRUE, warning=FALSE>>=
library(ggplot2)
ggplot(data, aes(x=period, y=values)) + 
  geom_line() + facet_wrap(~ Category, scales="free", ncol=2)
@


\end{document}