Add ci function

The ci function adds confidence interval and
relative frequencies to a table.

Change-Id: Id702522d35e557f20540bc24301195d0513b7138
diff --git a/man/ci.Rd b/man/ci.Rd
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+++ b/man/ci.Rd
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+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/ci.R
+\name{ci}
+\alias{ci}
+\title{Add confidence interval and relative frequency variables}
+\usage{
+ci(df, x = totalResults, N = tokens, conf.level = 0.95)
+}
+\arguments{
+\item{df}{table with columns for absolute and total frequencies.}
+
+\item{x}{column with the observed absolute frequency.}
+
+\item{N}{column with the total frequncies}
+
+\item{conf.level}{confidence level of the returned confidence interval. Must
+be a single number between 0 and 1.}
+}
+\description{
+Using \code{\link{prop.test}}, \code{ci} adds three columns to a data frame:
+1. relative frequency (\code{f}) 2. lower bound of a confidence interval
+(\code{ci.low}) 3. upper bound of a confidence interval
+}
+\examples{
+library(ggplot2)
+kco <- new("KorAPConnection", verbose=TRUE)
+expand_grid(year=2015:2018, alternatives=c("Hate Speech", "Hatespeech")) \%>\%
+  bind_cols(corpusQuery(kco, .$alternatives, sprintf("pubDate in \%d", .$year))) \%>\%
+  mutate(tokens=corpusStats(kco, vc=vc)$tokens) \%>\%
+  ci() \%>\%
+  ggplot(aes(x=year, y=f, fill=query, color=query, ymin=conf.low, ymax=conf.high)) +
+    geom_point() + geom_line() + geom_ribbon(alpha=.3)
+
+}