Barchart

Barchart

The Barchart node creates bar charts using ggplot2 to compare values across categories. It uses geom_bar(stat = "identity") so the bar heights represent actual values in your data.

What it does

• Creates a bar chart from a category variable (X) and a value variable (Y)
• Uses stat = "identity" so bars represent values directly from the data
• Optionally groups bars by a fill variable using position_dodge()
• Optionally adds error bars using geom_errorbar() with adjustable width
• Supports custom axis labels
• The plot can be downloaded as a PNG image

How to use it

1. Connect a data source — drag an edge from an Input CSV node
2. Select a category variable (X) — choose the column for the x axis categories
3. Select a value variable (Y) — choose the numeric column for bar heights
4. Optionally configure — set a fill variable for grouped bars, an error bar variable, or custom axis labels
5. Click Run — the bar chart is generated and displayed

Configuration

Setting	Required	Description
Upstream connection	Yes	A node providing data
Category variable (X)	Yes	Categorical variable for the x axis
Value variable (Y)	Yes	Numeric variable for bar heights
Fill variable	No	A grouping variable to create side-by-side (dodged) bars
Error bar variable	No	Column containing error values (e.g. SE) added/subtracted from Y
Error bar width	No	Width of error bar caps (default 0.3)
X axis label	No	Custom label (defaults to column name)
Y axis label	No	Custom label (defaults to column name)
Comment	No	Annotation for generated R code

Output

The Output tab displays:

• The bar chart as an image
• A Zoom button to view the plot full-screen
• A Download plot button to save it as a PNG file (named barchart_{y}_by_{x}.png)

Generated R code

Basic bar chart:

library(ggplot2)
ggplot(data = my_data, aes(x = species, y = count)) +
  geom_bar(stat = "identity") +
  theme_classic()

With fill variable and custom labels:

library(ggplot2)
ggplot(data = my_data, aes(x = species, y = count, fill = diet)) +
  geom_bar(stat = "identity", position = position_dodge()) +
  theme_classic() +
  labs(x = "Species", y = "Count")

With error bars:

library(ggplot2)
ggplot(data = my_data, aes(x = species, y = count, fill = diet)) +
  geom_bar(stat = "identity", position = position_dodge()) +
  geom_errorbar(aes(ymin = count - se, ymax = count + se), width = 0.3, position = position_dodge()) +
  theme_classic() +
  labs(x = "Species", y = "Count")

Tips

• The category variable (X) is typically categorical — it defines the groups along the x axis
• The value variable (Y) should be numeric — it defines the height of each bar
• Use the fill variable to create grouped (side-by-side) bars within each category using position_dodge()
• Without a fill variable, bars are stacked by default (one bar per category)
• Error bars show ± the error variable (e.g. standard error) around each bar height
• Adjust the error bar width to control how wide the caps appear (default 0.3)
• You can download the plot for use in reports or presentations