用R绘制坡度图-Slope Chart（一）

坡度图是比较几个点之间的相对位置的一个很好的方法，基本思想是利用折线图来呈现。下面我们以不同时间点的基因表达为例教大家如何绘制坡度图：

library(ggplot2)
library(ggthemes)

# 演示数据
df <- data.frame(
    A = c("GENE1", "GENE2", "GENE3", "GENE4", "GENE5"),
    B = c(31, 432, 54, 654, 76),
    C = c(4, 465, 65, 768, 87),
    D = c(32,499,65,657,87)
)

# 定义列名
colnames(df) <- c("GENE", "Time1", "Time2", "Time3")
# 定义标签
t1 <- paste(df$GENE, round(df$Time1), sep = ", ")
t2 <- paste(df$GENE, round(df$Time2), sep = ", ")
t3 <- paste(df$GENE, round(df$Time3), sep = ", ")
# 定义颜色
df$class <- ifelse((df$Time2 - df$Time1) < 0, "red", "green")

# 绘图
ggplot(df) + geom_segment( # 绘制Time1到Time2折线图
    aes(
        x = 1,
        xend = 2,
        y = Time1,
        yend = Time2,
        col = class
    ),
    size = .75,
    show.legend = F
) +
    geom_segment(# 绘制Time2到Time3折线图
        aes(
            x = 2,
            xend = 3,
            y = Time2,
            yend = Time3,
            col = class
        ),
        size = .75,
        show.legend = F
    ) +
    # 添加竖线
    geom_vline(xintercept = 1,
               # 竖线类型，虚线
               linetype = "dashed",
               size = .1) +
    geom_vline(xintercept = 2,
               linetype = "dashed",
               size = .1) +
    geom_vline(xintercept = 3,
               linetype = "dashed",
               size = .1) +
    scale_color_manual(
        labels = c("Up", "Down"),
        values = c("green" = "#00ba38", "red" =
                       "#f8766d")
    ) +  # color of lines
    labs(x = "Time", y = "GENE Count") +  # 坐标轴标签
    # 定义x、y轴范围
    xlim(0.5, 3.5) +
    ylim(0, (1.1 * (max(
        df$Time1, df$Time2, df$Time3
    )))) + # X and Y axis limits
    
    # 添加标签
    geom_text(
        label = t1,
        y = df$Time1,
        x = rep(1, NROW(df)),
        hjust = 1.1,
        size = 3.5
    ) +
    geom_text(
        label = t2,
        y = df$Time2,
        x = rep(2, NROW(df)),
        hjust = -0.1,
        size = 3.5
    ) +
    geom_text(
        label = t3,
        y = df$Time3,
        x = rep(3, NROW(df)),
        hjust = -0.1,
        size = 3.5
    ) +
    geom_text(
        label = "Time 1",
        x = 1,
        y = 1.1 * (max(df$Time1, df$Time2)),
        hjust = 1.2,
        size = 5
    ) + # title
    geom_text(
        label = "Time 2",
        x = 2,
        y = 1.1 * (max(df$Time1, df$Time2)),
        hjust = -0.1,
        size = 5
    ) +  # title
    geom_text(
        label = "Time 3",
        x = 3,
        y = 1.1 * (max(df$Time2, df$Time3)),
        hjust = -0.1,
        size = 5
    ) +
    # 主题
    theme_few()

这里主要用了ggplot2的geom_segment绘制，大家可以根据我给的示例代码学习掌握。

参考资料：

1.http://r-statistics.co/Top50-Ggplot2-Visualizations-MasterList-R-Code.html#Dot%20Plot