R 使用geom_iles在一个切片中包含多个值

我用geom_tile创建了一个矩阵曲线图，但是看到行有多个值在曲线图中重叠.有没有办法用代表该条目的多种 colored颜色 填充每个瓷砖？可能类似于此(理想情况下，形状应该是矩形而不是三角形):split fill in ggplot geom_tile (or heatmap): two colors by third value

代码:

# Create color palette

par(mar=c(0,0,1,0))

coul <- brewer.pal(9, "Set3") 

ggplot(plot_data, aes(x = from, y = to, fill = agreement_num)) +
  geom_tile() +
  scale_fill_manual(values = coul) +
  theme_bw() +
  scale_x_discrete(drop = FALSE) +
  scale_y_discrete(drop = FALSE) +
  theme(
    axis.text.x = element_text(size = 9,angle = 270, hjust = 0,vjust=0),
    axis.text.y = element_text(size = 9),
    aspect.ratio = 1)

可复制的示例:

plot_data <- structure(list(from = structure(c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, NA, NA, NA, NA), levels = c("Afghanistan", 
"Kazakhstan", "Kyrgyzstan", "Tajikistan", "Turkmenistan", "Uzbekistan"
), class = "factor"), to = structure(c(1L, 3L, 3L, 3L, 3L, 3L, 
3L, 4L, 4L, 4L, 5L, 5L, 6L, 6L, 2L, 6L, NA, NA, NA, NA), levels = c("Afghanistan", 
"Kazakhstan", "Kyrgyzstan", "Tajikistan", "Turkmenistan", "Uzbekistan"
), class = "factor"), weight = c(1291072130433.34, 480160896152.234, 
480160896152.234, 480160896152.234, 480160896152.234, 480160896152.234, 
480160896152.234, 3474907531417.02, 3474907531417.02, 3474907531417.02, 
867103764128.709, 867103764128.709, 7791981051421.92, 7791981051421.92, 
133799551.098735, 1102379004.66647, NA, NA, NA, NA), agreement_num = structure(c(NA, 
1L, 5L, 2L, 6L, 3L, 4L, 2L, 1L, 6L, 1L, 6L, 1L, 6L, NA, NA, NA, 
NA, NA, NA), levels = c("51", "58", "133", "135", "176", "224"
), class = "factor")), row.names = c("1", "2", "3", "4", "5", 
"6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", 
"NA", "NA.1", "NA.2", "NA.3"), class = "data.frame")