如何为Haskell plot库绘制的条形图X轴添加字符串标签？

使用plot库绘制条形图时，若想将X轴默认的数值刻度（如"1.00"）替换为"A"、"B"、"C"这类自定义字符串标签，可通过自定义X轴刻度实现。

你的原始代码如下：

import Graphics.Rendering.Plot.Figure
import Graphics.Rendering.Plot.Render
import Numeric.LinearAlgebra (vector, Vector)

test_bar :: Figure ()
test_bar = do
    let ts = vector [1..5] :: Vector Double
        ds = vector [1..5] :: Vector Double
        barWidth = 10 :: Double
        barBorder = 2 :: Double

    setPlots 1 1
    withPlot (1,1) $ do
        setDataset (ts,[bar ds (barWidth, grey::Color,barBorder)])
        addAxis XAxis (Side Lower) $ withAxisLabel $ setText "X-axis"
        addAxis YAxis (Side Lower) $ withAxisLabel $ setText "Y-axis"
        setRange XAxis Lower Linear 0 5
        setRange YAxis Lower Linear 0 5

main :: IO ()
main = do writeFigure PNG "bars.png" (w,h) test_bar
    where 
        w = 800
        h = 600

修改方案 #

核心是利用setTicks函数绑定X轴位置与自定义字符串标签，具体修改如下：

import Graphics.Rendering.Plot.Figure
import Graphics.Rendering.Plot.Render
import Numeric.LinearAlgebra (vector, Vector, toList)
import Graphics.Rendering.Plot.Types (textTick)

test_bar :: Figure ()
test_bar = do
    let ts = vector [1..5] :: Vector Double
        ds = vector [1..5] :: Vector Double
        barWidth = 10 :: Double
        barBorder = 2 :: Double
        -- 定义与条形位置对应的字符串标签
        labels = ["A", "B", "C", "D", "E"]

    setPlots 1 1
    withPlot (1,1) $ do
        setDataset (ts,[bar ds (barWidth, grey::Color,barBorder)])
        -- 配置X轴，添加自定义刻度
        addAxis XAxis (Side Lower) $ do
            withAxisLabel $ setText "X-axis"
            -- 将每个条形的X位置与标签绑定，生成自定义刻度
            let customTicks = zip (toList ts) (map textTick labels)
            setTicks customTicks
        addAxis YAxis (Side Lower) $ withAxisLabel $ setText "Y-axis"
        -- 调整X轴范围，避免右侧标签被截断
        setRange XAxis Lower Linear 0 6
        setRange YAxis Lower Linear 0 5

main :: IO ()
main = writeFigure PNG "bars.png" (w,h) test_bar
    where 
        w = 800
        h = 600

关键修改说明 #

1. 新增导入：导入toList（将Vector转为普通列表）和textTick（创建文本类型的刻度对象）
2. 定义标签列表：labels中的每个元素对应ts里的一个条形位置
3. 设置自定义刻度：通过zip将X轴位置与文本标签配对，再用setTicks替换默认刻度
4. 调整X轴范围：将X轴上限从5改为6，避免最右侧的标签被图表边缘遮挡

内容的提问来源于stack exchange，提问作者Pompan