added vignette of freq

.gitignore

@@ -4,3 +4,4 @@
 .Ruserdata
 AMR.Rproj
 tests/testthat/Rplots.pdf
+inst/doc

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: AMR
-Version: 0.2.0
-Date: 2018-05-02
+Version: 0.2.0.9000
+Date: 2018-05-09
 Title: Antimicrobial Resistance Analysis
 Authors@R: c(
     person(
@@ -37,7 +37,10 @@ Imports:
     tibble
 Suggests:
     testthat (>= 1.0.2),
-    covr (>= 3.0.1)
+    covr (>= 3.0.1),
+    knitr,
+    rmarkdown
+VignetteBuilder: knitr
 URL: https://github.com/msberends/AMR
 BugReports: https://github.com/msberends/AMR/issues
 License: GPL-2 | file LICENSE

NEWS.md

@@ -1,4 +1,13 @@
-# 0.2.0
+# 0.2.9000 (development version)
+#### New
+* Vignettes about frequency tables: [vignettes/freq.html](vignettes/freq.html)
+* Possibility to globally set the default for the amount of items to print in frequency tables (`freq` function), with `options(max.print.freq = n)`
+
+#### Changed
+* Renamed `toConsole` parameter of `freq` to `as.data.frame`
+* Small translational improvements to the `septic_patients` dataset
+
+# 0.2.0 (latest stable version)
 #### New
 * Full support for Windows, Linux and macOS
 * Full support for old R versions, only R-3.0.0 (April 2013) or later is needed (needed packages may have other dependencies)

R/freq.R

@@ -21,10 +21,10 @@
 #' Create a frequency table of a vector of data, a single column or a maximum of 9 columns of a data frame. Supports markdown for reports.
 #' @param x data
 #' @param sort.count Sort on count. Use \code{FALSE} to sort alphabetically on item.
-#' @param nmax number of row to print. Use \code{nmax = 0} or \code{nmax = NA} to print all rows.
-#' @param na.rm a logical value indicating whether NA values should be removed from the frequency table. The header will always print the amount of\code{NA}s.
+#' @param nmax number of row to print. The default, \code{15}, uses \code{\link[base]{getOption}("max.print.freq")}. Use \code{nmax = 0} or \code{nmax = NA} to print all rows.
+#' @param na.rm a logical value indicating whether NA values should be removed from the frequency table. The header will always print the amount of \code{NA}s.
 #' @param markdown print table in markdown format (this forces \code{nmax = NA})
-#' @param toConsole Print table to the console. Use \code{FALSE} to assign the table to an object.
+#' @param as.data.frame return frequency table without header as a \code{data.frame} (e.g. to assign the table to an object)
 #' @param digits how many significant digits are to be used for numeric values (not for the items themselves, that depends on \code{\link{getOption}("digits")})
 #' @param sep a character string to separate the terms when selecting multiple columns
 #' @details For numeric values, the next values will be calculated and shown into the header:
@@ -32,7 +32,7 @@
 #'   \item{Mean, using \code{\link[base]{mean}}}
 #'   \item{Standard deviation, using \code{\link[stats]{sd}}}
 #'   \item{Five numbers of Tukey (min, Q1, median, Q3, max), using \code{\link[stats]{fivenum}}}
-#'   \item{Outliers (count and list), using \code{\link{boxplot.stats}}}
+#'   \item{Outliers (total count and unique count), using \code{\link{boxplot.stats}}}
 #'   \item{Coefficient of variation (CV), the standard deviation divided by the mean}
 #'   \item{Coefficient of quartile variation (CQV, sometimes called coefficient of dispersion), calculated as \code{(Q3 - Q1) / (Q3 + Q1)} using \code{\link{quantile}} with \code{type = 6} as quantile algorithm to comply with SPSS standards}
 #' }
@@ -63,13 +63,13 @@
 #' years <- septic_patients %>%
 #'   mutate(year = format(date, "%Y")) %>%
 #'   select(year) %>%
-#'   freq(toConsole = FALSE)
+#'   freq(as.data.frame = TRUE)
 freq <- function(x,
                  sort.count = TRUE,
-                 nmax = 15,
+                 nmax = getOption("max.print.freq"),
                  na.rm = TRUE,
                  markdown = FALSE,
-                 toConsole = TRUE,
+                 as.data.frame = FALSE,
                  digits = 2,
                  sep = " ") {
 
@@ -156,8 +156,8 @@ freq <- function(x,
       stop('A maximum of 9 columns can be analysed at the same time.', call. = FALSE)
     }
   }
-  if (markdown == TRUE & toConsole == FALSE) {
-    warning('`toConsole = FALSE` will be ignored when `markdown = TRUE`.')
+  if (markdown == TRUE & as.data.frame == TRUE) {
+    warning('`as.data.frame = TRUE` will be ignored when `markdown = TRUE`.')
   }
 
   if (mult.columns > 1) {
@@ -232,7 +232,7 @@ freq <- function(x,
     x <- x %>% format(formatdates)
   }
 
-  if (toConsole == TRUE) {
+  if (as.data.frame == FALSE) {
     cat(header)
   }
 
@@ -244,22 +244,30 @@ freq <- function(x,
     warning('All observations are unique.', call. = FALSE)
   }
 
-  if (nmax == 0 | is.na(nmax)) {
+  nmax.set <- !missing(nmax)
+  if (is.null(nmax) & is.null(base::getOption("max.print.freq", default = NULL))) {
+    # default for max print setting
+    nmax <- 15
+  }
+
+  if (nmax == 0 | is.na(nmax) | is.null(nmax)) {
     nmax <- length(x)
   }
   nmax.1 <- min(length(x), nmax + 1)
 
   # create table with counts and percentages
+  column_names <- c('Item', 'Count', 'Percent', 'Cum. Count', 'Cum. Percent', '(Factor Level)')
+  column_names_df <- c('item', 'count', 'percent', 'cum_count', 'cum_percent', 'factor_level')
   if (any(class(x) == 'factor')) {
     df <- tibble::tibble(Item = x,
                          Fctlvl = x %>% as.integer()) %>%
       group_by(Item, Fctlvl)
-    column_names <- c('Item', 'Count', 'Percent', 'Cum. Count', 'Cum. Percent', '(Factor Level)')
     column_align <- c('l', 'r', 'r', 'r', 'r', 'r')
   } else {
     df <- tibble::tibble(Item = x) %>%
       group_by(Item)
-    column_names <- c('Item', 'Count', 'Percent', 'Cum. Count', 'Cum. Percent')
+    column_names <- column_names[1:5] # strip factor lvl
+    column_names_df <- column_names_df[1:5] # strip factor lvl
     column_align <- c(x_align, 'r', 'r', 'r', 'r')
   }
   df <- df %>%
@@ -276,10 +284,10 @@ freq <- function(x,
 
   # sort according to setting
   if (sort.count == TRUE) {
-    df <- df %>% arrange(desc(Count))
+    df <- df %>% arrange(desc(Count), Item)
   } else {
     if (any(class(x) == 'factor')) {
-      df <- df %>% arrange(Fctlvl)
+      df <- df %>% arrange(Fctlvl, Item)
     } else {
       df <- df %>% arrange(Item)
     }
@@ -295,65 +303,68 @@ freq <- function(x,
     df <- df %>% select(Item, Count, Percent, Cum, CumTot, Fctlvl)
   }
 
+  if (as.data.frame == TRUE) {
+    # assign to object
+    df[, 3] <- df[, 2] / sum(df[, 2], na.rm = TRUE)
+    df[, 4] <- cumsum(df[, 2])
+    df[, 5] <- df[, 4] / sum(df[, 2], na.rm = TRUE)
+    colnames(df) <- column_names_df
+    return(as.data.frame(df, stringsAsFactors = FALSE))
+  }
+
   if (markdown == TRUE) {
     tblformat <- 'markdown'
   } else {
     tblformat <- 'pandoc'
   }
 
-  if (toConsole == FALSE) {
-    # assign to object
-    df[, 3] <- df[, 2] / sum(df[, 2], na.rm = TRUE)
-    df[, 4] <- cumsum(df[, 2])
-    df[, 5] <- df[, 4] / sum(df[, 2], na.rm = TRUE)
-    return(df)
+  # save old NA setting for kable
+  opt.old <- options()$knitr.kable.NA
+  options(knitr.kable.NA = "<NA>")
 
-  } else {
+  Count.rest <- sum(df[nmax.1:nrow(df), 'Count'], na.rm = TRUE)
+  if (any(class(x) %in% c('double', 'integer', 'numeric', 'raw', 'single'))) {
+    df <- df %>% mutate(Item = format(Item))
+  }
+  df <- df %>% mutate(Count = format(Count))
 
-    # save old NA setting for kable
-    opt.old <- options()$knitr.kable.NA
-    options(knitr.kable.NA = "<NA>")
-
-    Count.rest <- sum(df[nmax.1:nrow(df), 'Count'], na.rm = TRUE)
-    if (any(class(x) %in% c('double', 'integer', 'numeric', 'raw', 'single'))) {
-      df <- df %>% mutate(Item = format(Item))
-    }
-    df <- df %>% mutate(Count = format(Count))
-
-    if (nrow(df) > nmax.1 & markdown == FALSE) {
-      df2 <- df[1:nmax,]
-      print(
-        knitr::kable(df2,
-                     format = tblformat,
-                     col.names = column_names,
-                     align = column_align,
-                     padding = 1)
-      )
-      cat('... and ',
-          format(nrow(df) - nmax),
-          ' more ',
-          paste0('(n = ',
-                 format(Count.rest),
-                 '; ',
-                 (Count.rest / length(x)) %>% percent(force_zero = TRUE),
-                 ')'),
-          '. Use `nmax` to show more rows.\n', sep = '')
-
-    } else {
-      print(
-        knitr::kable(df,
-                     format = tblformat,
-                     col.names = column_names,
-                     align = column_align,
-                     padding = 1)
-      )
+  if (nrow(df) > nmax.1 & markdown == FALSE) {
+    df2 <- df[1:nmax,]
+    print(
+      knitr::kable(df2,
+                   format = tblformat,
+                   col.names = column_names,
+                   align = column_align,
+                   padding = 1)
+    )
+    cat('... and ',
+        format(nrow(df) - nmax),
+        ' more ',
+        paste0('(n = ',
+               format(Count.rest),
+               '; ',
+               (Count.rest / length(x)) %>% percent(force_zero = TRUE),
+               ')'),
+        '.', sep = '')
+    if (nmax.set == FALSE) {
+      cat(' Use `nmax` to show more or less rows.')
     }
     cat('\n')
 
-    # reset old kable setting
-    options(knitr.kable.NA = opt.old)
-    return(invisible())
+  } else {
+    print(
+      knitr::kable(df,
+                   format = tblformat,
+                   col.names = column_names,
+                   align = column_align,
+                   padding = 1)
+    )
   }
+  cat('\n')
+
+  # reset old kable setting
+  options(knitr.kable.NA = opt.old)
+  return(invisible())
 }
 
 #' @rdname freq

README.md

@@ -3,7 +3,7 @@
 
 [![logo_rug](man/figures/logo_rug.png)](https://www.rug.nl)[![logo_umcg](man/figures/logo_umcg.png)](https://www.umcg.nl)
 
-This R package was created for academic research by PhD students of the Faculty of Medical Sciences of the [University of Groningen)](https://www.rug.nl) and the Medical Microbiology & Infection Prevention (MMBI) department of the [University Medical Center Groningen (UMCG)](https://www.umcg.nl). See [Authors](#authors).
+This R package was created for academic research by PhD students of the Faculty of Medical Sciences of the [University of Groningen](https://www.rug.nl) and the Medical Microbiology & Infection Prevention (MMBI) department of the [University Medical Center Groningen (UMCG)](https://www.umcg.nl). See [Authors](#authors).
 
 ## Why this package?
 This R package contains functions to make **microbiological, epidemiological data analysis easier**. It allows the use of some new classes to work with MIC values and antimicrobial interpretations (i.e. values S, I and R).

man/freq.Rd

@@ -5,24 +5,26 @@
 \alias{frequency_tbl}
 \title{Frequency table}
 \usage{
-freq(x, sort.count = TRUE, nmax = 15, na.rm = TRUE, markdown = FALSE,
-  toConsole = TRUE, digits = 2, sep = " ")
+freq(x, sort.count = TRUE, nmax = getOption("max.print.freq"),
+  na.rm = TRUE, markdown = FALSE, as.data.frame = FALSE, digits = 2,
+  sep = " ")
 
-frequency_tbl(x, sort.count = TRUE, nmax = 15, na.rm = TRUE,
-  markdown = FALSE, toConsole = TRUE, digits = 2, sep = " ")
+frequency_tbl(x, sort.count = TRUE, nmax = getOption("max.print.freq"),
+  na.rm = TRUE, markdown = FALSE, as.data.frame = FALSE, digits = 2,
+  sep = " ")
 }
 \arguments{
 \item{x}{data}
 
 \item{sort.count}{Sort on count. Use \code{FALSE} to sort alphabetically on item.}
 
-\item{nmax}{number of row to print. Use \code{nmax = 0} or \code{nmax = NA} to print all rows.}
+\item{nmax}{number of row to print. The default, \code{15}, uses \code{\link[base]{getOption}("max.print.freq")}. Use \code{nmax = 0} or \code{nmax = NA} to print all rows.}
 
-\item{na.rm}{a logical value indicating whether NA values should be removed from the frequency table. The header will always print the amount of\code{NA}s.}
+\item{na.rm}{a logical value indicating whether NA values should be removed from the frequency table. The header will always print the amount of \code{NA}s.}
 
 \item{markdown}{print table in markdown format (this forces \code{nmax = NA})}
 
-\item{toConsole}{Print table to the console. Use \code{FALSE} to assign the table to an object.}
+\item{as.data.frame}{return frequency table without header as a \code{data.frame} (e.g. to assign the table to an object)}
 
 \item{digits}{how many significant digits are to be used for numeric values (not for the items themselves, that depends on \code{\link{getOption}("digits")})}
 
@@ -37,7 +39,7 @@ For numeric values, the next values will be calculated and shown into the header
   \item{Mean, using \code{\link[base]{mean}}}
   \item{Standard deviation, using \code{\link[stats]{sd}}}
   \item{Five numbers of Tukey (min, Q1, median, Q3, max), using \code{\link[stats]{fivenum}}}
-  \item{Outliers (count and list), using \code{\link{boxplot.stats}}}
+  \item{Outliers (total count and unique count), using \code{\link{boxplot.stats}}}
   \item{Coefficient of variation (CV), the standard deviation divided by the mean}
   \item{Coefficient of quartile variation (CQV, sometimes called coefficient of dispersion), calculated as \code{(Q3 - Q1) / (Q3 + Q1)} using \code{\link{quantile}} with \code{type = 6} as quantile algorithm to comply with SPSS standards}
 }
@@ -63,7 +65,7 @@ septic_patients \%>\%
 years <- septic_patients \%>\%
   mutate(year = format(date, "\%Y")) \%>\%
   select(year) \%>\%
-  freq(toConsole = FALSE)
+  freq(as.data.frame = TRUE)
 }
 \keyword{freq}
 \keyword{frequency}

tests/testthat/test-eucast.R

@@ -1,7 +1,7 @@
 context("eucast.R")
 
 test_that("EUCAST rules work", {
-  a <- EUCAST_rules(septic_patients)
+  a <- suppressWarnings(EUCAST_rules(septic_patients))
 
   a <- data.frame(bactid = c("KLEPNE",  # Klebsiella pneumoniae
                              "PSEAER",  # Pseudomonas aeruginosa

tests/testthat/test-freq.R

@@ -1,12 +1,12 @@
 context("freq.R")
 
 test_that("frequency table works", {
-  expect_equal(nrow(freq(c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5), toConsole = FALSE)), 5)
-  expect_equal(nrow(frequency_tbl(c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5), toConsole = FALSE)), 5)
+  expect_equal(nrow(freq(c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5), as.data.frame = TRUE)), 5)
+  expect_equal(nrow(frequency_tbl(c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5), as.data.frame = TRUE)), 5)
 
   # date column of septic_patients should contain 1662 unique dates
-  expect_equal(nrow(freq(septic_patients$date, toConsole = FALSE)), 1662)
-  expect_equal(nrow(freq(septic_patients$date, toConsole = FALSE)),
+  expect_equal(nrow(freq(septic_patients$date, as.data.frame = TRUE)), 1662)
+  expect_equal(nrow(freq(septic_patients$date, as.data.frame = TRUE)),
                length(unique(septic_patients$date)))
 
   expect_output(freq(septic_patients$age))

tests/testthat/test-mdro.R

@@ -13,7 +13,7 @@ test_that("MDRO works", {
   expect_equal(outcome %>% class(), c('ordered', 'factor'))
 
   # septic_patients should have these finding using Dutch guidelines
-  expect_equal(outcome %>% freq(toConsole = FALSE) %>% pull(Count), c(3, 21))
+  expect_equal(outcome %>% freq(as.data.frame = TRUE) %>% pull(count), c(3, 21))
 
   expect_equal(BRMO(septic_patients, info = FALSE), MDRO(septic_patients, "nl", info = FALSE))
 

vignettes/freq.R

@@ -0,0 +1,91 @@
+## ----setup, include = FALSE, results = 'markup'--------------------------
+knitr::opts_chunk$set(
+  collapse = TRUE,
+  comment = "#"
+)
+library(dplyr)
+library(AMR)
+
+## ---- echo = TRUE, results = 'hide'--------------------------------------
+# # just using base R
+freq(septic_patients$sex)
+
+# # using base R to select the variable and pass it on with a pipe
+septic_patients$sex %>% freq()
+
+# # do it all with pipes, using the `select` function of the dplyr package
+septic_patients %>%
+  select(sex) %>%
+  freq()
+
+## ---- echo = TRUE--------------------------------------------------------
+freq(septic_patients$sex)
+
+## ---- echo = TRUE, results = 'hide'--------------------------------------
+my_patients <- septic_patients %>% 
+  left_join_microorganisms()
+
+## ---- echo = TRUE--------------------------------------------------------
+colnames(microorganisms)
+
+## ---- echo = TRUE--------------------------------------------------------
+dim(septic_patients)
+dim(my_patients)
+
+## ---- echo = TRUE--------------------------------------------------------
+my_patients %>%
+  select(genus, species) %>%
+  freq()
+
+## ---- echo = TRUE--------------------------------------------------------
+# # get age distribution of unique patients
+septic_patients %>% 
+  distinct(patient_id, .keep_all = TRUE) %>% 
+  select(age) %>% 
+  freq(nmax = 5)
+
+## ---- echo = TRUE--------------------------------------------------------
+septic_patients %>%
+  select(hospital_id) %>% 
+  freq()
+
+## ---- echo = TRUE--------------------------------------------------------
+septic_patients %>%
+  select(hospital_id) %>% 
+  freq(sort.count = TRUE)
+
+## ---- echo = TRUE--------------------------------------------------------
+septic_patients %>%
+  select(amox) %>% 
+  freq()
+
+## ---- echo = TRUE--------------------------------------------------------
+septic_patients %>%
+  select(date) %>% 
+  freq(nmax = 5)
+
+## ---- echo = TRUE--------------------------------------------------------
+septic_patients %>%
+  select(amox) %>% 
+  freq(na.rm = FALSE)
+
+## ---- echo = TRUE--------------------------------------------------------
+septic_patients %>%
+  select(hospital_id) %>% 
+  freq(markdown = TRUE)
+
+## ---- echo = TRUE--------------------------------------------------------
+my_df <- septic_patients %>%
+  select(hospital_id) %>% 
+  freq(as.data.frame = TRUE)
+
+my_df
+
+class(my_df)
+
+## ---- echo = FALSE-------------------------------------------------------
+# this will print "2018" in 2018, and "2018-yyyy" after 2018.
+yrs <- c(2018:format(Sys.Date(), "%Y"))
+yrs <- c(min(yrs), max(yrs))
+yrs <- paste(unique(yrs), collapse = "-")
+

vignettes/freq.Rmd

@@ -0,0 +1,183 @@
+---
+title: "Creating Frequency Tables"
+author: "Matthijs S. Berends"
+output: 
+  rmarkdown::html_vignette:
+    toc: true
+vignette: >
+  %\VignetteIndexEntry{Vignette Title}
+  %\VignetteEngine{knitr::rmarkdown}
+  %\VignetteEncoding{UTF-8}
+---
+
+```{r setup, include = FALSE, results = 'markup'}
+knitr::opts_chunk$set(
+  collapse = TRUE,
+  comment = "#"
+)
+library(dplyr)
+library(AMR)
+```
+
+## Introduction
+
+Frequency tables (or frequency distributions) are summaries of the distribution of values in a sample. With the `freq` function, you can create univariate frequency tables. Multiple variables will be pasted into one variable, so it forces a univariate distribution. We take the `septic_patients` dataset (included in this AMR package) as example.
+
+## Frequencies of one variable
+
+To only show and quickly review the content of one variable, you can just select this variable in various ways. Let's say we want to get the frequencies of the `sex` variable of the `septic_patients` dataset:
+```{r, echo = TRUE, results = 'hide'}
+# # just using base R
+freq(septic_patients$sex)
+
+# # using base R to select the variable and pass it on with a pipe
+septic_patients$sex %>% freq()
+
+# # do it all with pipes, using the `select` function of the dplyr package
+septic_patients %>%
+  select(sex) %>%
+  freq()
+```
+This will all lead to the following table:
+```{r, echo = TRUE}
+freq(septic_patients$sex)
+```
+This immediately shows the class of the variable, its length and availability (i.e. the amount of `NA`), the amount of unique values and (most importantly) that among septic patients men are more prevalent than women.
+
+## Frequencies of more than one variable
+
+Multiple variables will be pasted into one variable to review individual cases, keeping a univariate frequency table.
+
+For illustration, we could add some more variables to the `septic_patients` dataset to learn about bacterial properties:
+```{r, echo = TRUE, results = 'hide'}
+my_patients <- septic_patients %>% 
+  left_join_microorganisms()
+```
+Now all variables of the `microorganisms` dataset have been joined to the `septic_patients` dataset. The `microorganisms` dataset consists of the following variables:
+```{r, echo = TRUE}
+colnames(microorganisms)
+```
+
+If we compare the dimensions between the old and new dataset, we can see that these `r ncol(my_patients) - ncol(septic_patients)` variables were added:
+```{r, echo = TRUE}
+dim(septic_patients)
+dim(my_patients)
+```
+
+So now the `genus` and `species` variables are available. A frequency table of these combined variables can be created like this:
+```{r, echo = TRUE}
+my_patients %>%
+  select(genus, species) %>%
+  freq()
+```
+
+## Frequencies of numeric values
+
+Frequency tables can be created of any input.
+
+In case of numeric values (like integers, doubles, etc.) additional descriptive statistics will be calculated and shown into the header:
+
+```{r, echo = TRUE}
+# # get age distribution of unique patients
+septic_patients %>% 
+  distinct(patient_id, .keep_all = TRUE) %>% 
+  select(age) %>% 
+  freq(nmax = 5)
+```
+
+So the following properties are determined, where `NA` values are always ignored:
+
+* **Mean**
+
+* **Standard deviation**
+
+* **Coefficient of variation** (CV), the standard deviation divided by the mean
+
+* **Five numbers of Tukey** (min, Q1, median, Q3, max)
+
+* **Coefficient of quartile variation** (CQV, sometimes called coefficient of dispersion), calculated as (Q3 - Q1) / (Q3 + Q1) using quantile with `type = 6` as quantile algorithm to comply with SPSS standards
+
+* **Outliers** (total count and unique count)
+
+So for example, the above frequency table quickly shows the median age of patients being `r my_patients %>% distinct(patient_id, .keep_all = TRUE) %>% pull(age) %>% median(na.rm = TRUE)`.
+
+## Frequencies of factors
+
+Frequencies of factors will be sorted on factor level instead of item count by default. This can be changed with the `sort.count` parameter. Frequency tables of factors always show the factor level as an additional last column.
+
+`sort.count` is `TRUE` by default, except for factors. Compare this default behaviour:
+
+```{r, echo = TRUE}
+septic_patients %>%
+  select(hospital_id) %>% 
+  freq()
+```
+
+To this, where items are now sorted on item count:
+
+```{r, echo = TRUE}
+septic_patients %>%
+  select(hospital_id) %>% 
+  freq(sort.count = TRUE)
+```
+
+All classes will be printed into the header. Variables with the new `rsi` class of this AMR package are actually ordered factors and have three classes (look at `Class` in the header):
+
+```{r, echo = TRUE}
+septic_patients %>%
+  select(amox) %>% 
+  freq()
+```
+
+## Frequencies of dates
+
+Frequencies of dates will show the oldest and newest date in the data, and the amount of days between them:
+
+```{r, echo = TRUE}
+septic_patients %>%
+  select(date) %>% 
+  freq(nmax = 5)
+```
+
+## Additional parameters
+
+### Parameter `na.rm`
+With the `na.rm` parameter (defaults to `TRUE`, but they will always be shown into the header), you can include `NA` values in the frequency table:
+```{r, echo = TRUE}
+septic_patients %>%
+  select(amox) %>% 
+  freq(na.rm = FALSE)
+```
+
+### Parameter `markdown`
+The `markdown` parameter can be used in reports created with R Markdown. This will always print all rows:
+
+```{r, echo = TRUE}
+septic_patients %>%
+  select(hospital_id) %>% 
+  freq(markdown = TRUE)
+```
+
+### Parameter `as.data.frame`
+With the `as.data.frame` parameter you can assign the frequency table to an object, or just print it as a `data.frame` to the console:
+
+```{r, echo = TRUE}
+my_df <- septic_patients %>%
+  select(hospital_id) %>% 
+  freq(as.data.frame = TRUE)
+
+my_df
+
+class(my_df)
+```
+
+----
+```{r, echo = FALSE}
+# this will print "2018" in 2018, and "2018-yyyy" after 2018.
+yrs <- c(2018:format(Sys.Date(), "%Y"))
+yrs <- c(min(yrs), max(yrs))
+yrs <- paste(unique(yrs), collapse = "-")
+```
+AMR, (c) `r yrs`, `r packageDescription("AMR")$URL`
+
+Licensed under the [GNU General Public License v2.0](https://github.com/msberends/AMR/blob/master/LICENSE).