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Stacked Bar Chart of Item Response Distributions

Source: R/data_plots.R
plot_stackedbars.Rd

Creates a horizontal stacked bar chart showing the response distribution for all items. Each bar represents one item, with segments colored by response category. Counts are displayed as text labels within each segment. This is a descriptive data visualization tool intended for use before model fitting.

Usage

plot_stackedbars(
  data,
  item_labels = NULL,
  category_labels = NULL,
  show_n = TRUE,
  show_percent = FALSE,
  text_color = "sienna1",
  text_size = 3,
  min_label_n = 0,
  viridis_option = "D",
  viridis_end = 0.99,
  title = "Item responses"
)

Arguments

data

A data frame in wide format containing only the item response columns. Each column is one item, each row is one person. All columns must be numeric (integer-valued). Response categories may be coded starting from 0 or 1. Do not include person IDs, grouping variables, or other non-item columns.

item_labels

An optional character vector of descriptive labels for the items (y-axis). Must be the same length as ncol(data). If NULL (the default), column names are used.

category_labels

An optional character vector of labels for the response categories (legend). Must be the same length as the number of response categories spanning from the minimum to the maximum observed value, ordered from lowest to highest category. If NULL (the default), numeric category values are used.

show_n

Logical. If TRUE (the default), the count of responses is displayed as a text label inside each bar segment.

show_percent

Logical. If TRUE, the percentage of responses is displayed instead of (or in addition to) counts. Default is FALSE.

text_color

Character. Color for the count/percentage labels. Default is "sienna1".

text_size

Numeric. Size of the count/percentage labels. Default is 3.

min_label_n

Integer. Minimum count required for a label to be displayed within a bar segment. Segments with fewer responses are left unlabelled to avoid clutter. Default is 0 (all segments labelled).

viridis_option

Character. Viridis palette option. One of "A" through "H". Default is "D".

viridis_end

Numeric in \([0, 1]\). End point of the viridis color scale. Default is 0.99.

title

Character. Plot title. Default is "Item responses".

Value

A ggplot object.

Details

Items are displayed on the y-axis in the same order as the columns in data (first column at the top). Each bar is divided into segments representing response categories, with the lowest category on the left and the highest on the right. The total bar length equals the number of non-missing responses for that item.

Categories with zero responses still appear in the legend but produce no visible bar segment, which helps identify gaps in the response distribution.

Input requirements:

  • All columns must be numeric (integer-valued).

  • The data frame must contain at least 2 columns (items) and at least 1 row (person).

Examples

library(ggplot2)
if (requireNamespace("eRm", quietly = TRUE))

# Basic stacked bar chart
plot_stackedbars(eRm::pcmdat2)


# With custom item and category labels
plot_stackedbars(
  eRm::pcmdat2,
  item_labels = c("Mood", "Sleep", "Appetite", "Energy"),
  category_labels = c("Never", "Sometimes", "Often")
)


# Show percentages, suppress small segments
plot_stackedbars(
  eRm::pcmdat2,
  show_percent = TRUE,
  show_n       = FALSE,
  min_label_n  = 5
)