plot_freq: Plot frequencies of a variable, optionally by group (histogram without binning)

Description

Creates a frequency plot showing the frequency of every observed value, displaying the full range from minimum to maximum value.

Usage

plot_freq(
  formula,
  y = NULL,
  data = NULL,
  labels = NULL,
  freq = TRUE,
  order = NULL,
  col = "dodgerblue",
  lwd = 9,
  width = NULL,
  value.labels = TRUE,
  add = FALSE,
  show.legend = TRUE,
  legend.title = NULL,
  col.text = NULL,
  ...
)

Value

Invisibly returns a data frame with values and their frequencies.

Arguments

formula: A formula of the form x ~ group where x is the variable to plot frequencies for and group is an optional grouping variable (with 2 or 3 unique values). For single variable (no grouping), use x ~ 1. Alternatively, pass a single vector x for a simple frequency plot.
y: An optional second vector to compare with formula. When provided, creates a comparison plot of two variables (like grouped plot but with separate variables). This allows syntax like plot_freq(y1, y2) to compare two vectors.
data: An optional data frame containing the variables in the formula.
labels: An optional character vector of length 2 providing custom labels for the two vectors when using two-vector syntax. Only applicable when y is provided. If NULL (default), uses the variable names. If data is not provided, variables are evaluated from the calling environment.
freq: Logical. If TRUE (default), displays frequencies. If FALSE, displays percentages.
order: Controls the order in which groups appear in the plot and legend. Use -1 to reverse the default order. Alternatively, provide a vector specifying the exact order (e.g., c("B", "A", "C")). If NULL (default), groups are ordered by their factor levels (if the grouping variable is a factor) or sorted alphabetically/numerically. Only applies when using grouped plots or comparing two variables.
col: Color for the bars.
lwd: Line width for the frequency bars. Default is 9.
width: Numeric. Width of the frequency bars. If NULL (default), width is automatically calculated based on the spacing between values.
value.labels: Logical. If TRUE, displays frequencies on top of each line.
add: Logical. If TRUE, adds to an existing plot instead of creating a new one.
show.legend: Logical. If TRUE (default), displays a legend when group is specified. If FALSE, no legend is shown.
legend.title: Character string. Title for the legend when group is specified. If NULL (default), no title is shown.
col.text: Color for the value labels. If not specified, uses col for non-grouped plots or group colors for grouped plots.
...: Pass on any argument accepted by plot() e.g., xlab='x-axis' , main='Distribution of X'

Details

This function creates a frequency plot where each observed value is shown with its frequency. Unlike a standard histogram, there is no binning, unlike a barplot, non-observed values of the variable are shown with 0 frequency instead of skipped.

Examples

Run this code

# Simple example
x <- c(1, 1, 2, 2, 2, 5, 5)
plot_freq(x)

# Pass on some common \code{plot()} arguments
plot_freq(x, col = "steelblue", xlab = "Value", ylab = "Frequency",ylim=c(0,7))

# Add to an existing plot
plot_freq(x, col = "dodgerblue")
plot_freq(x + 1, col = "red", add = TRUE)

# Compare two vectors
y1 <- c(1, 1, 2, 2, 2, 5, 5)
y2 <- c(1, 2, 2, 3, 3, 3)
plot_freq(y1, y2)

# Compare two vectors with custom labels
plot_freq(y1, y2, labels = c("men", "women"))

# Using a data frame with grouping
df <- data.frame(value = c(1, 1, 2, 2, 2, 5, 5), group = c("A", "A", "A", "B", "B", "A", "B"))
plot_freq(value ~ 1, data = df)  # single variable
plot_freq(value ~ group, data = df)  # with grouping

# Control group order in legend and plot
plot_freq(value ~ group, data = df, order = c("B", "A"))  # B first, then A
plot_freq(value ~ group, data = df, order = -1)  # Reverse default order

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