R 如何增加ggplot2图例大小以将图形导出为png？

我正试图导出一张我为演讲制作的图表，比较植物对不同肥料处理的平均反应。我使用R png函数导出图像，我需要它的大小在下面的代码中定义。我唯一不知道怎么做的就是增加图例的大小，使其看起来更大，就像图中的其余部分一样。我该怎么做

数据：

---

dataset多亏了上面的评论，我用
legend.key.size
、
legend.text
和
legend.title
添加内容更新了我的代码，它完全满足了我的需要

ggplot(datasetMean, aes(x = cultivar, y = vi, fill=factor(rate)))+
  geom_bar(stat="identity", width = 0.6, position = "dodge", col = "black")+
  scale_fill_discrete(name = "Rate", labels = c("0X","1X","4X","8X"))+
  xlab("Cultivar") + ylab("vi")+
  ggtitle("VI Scores")+
  theme(plot.title = element_text(hjust = 0.5, size = 30),
        strip.text.x = element_text(size = 25),
        axis.text = element_text(size = 20),
        axis.title = element_text(size = 25),
        legend.key.size = unit(1.5, "cm"),
        legend.text = element_text(size = 15),
        legend.title = element_text(size = 20),
        axis.title.y = element_text(angle = 0))

您是否尝试过调整主题中的
图例.key.size
？更多信息：@ravic_uu这就是解决方案。非常感谢。
#Aggregate data frame
datasetMean <- aggregate.data.frame(dataset, by=list(dataset$cultivar, dataset$rate), mean)
datasetMean <- select(datasetMean, Group.1, Group.2, vi)
colnames(datasetMean) <- c("cultivar","rate","vi")


#Generate graph and export graph as png
png("scores.png", width = 1000, height = 700)

ggplot(datasetMean, aes(x = cultivar, y = vi, fill=factor(rate)))+
  geom_bar(stat="identity", width = 0.6, position = "dodge", col = "black")+
  scale_fill_discrete(name = "Rate", labels = c("10","20","30","40"))+
  xlab("Cultivar") + ylab("vi") +
  ggtitle("VI Scores")+
  theme(plot.title = element_text(hjust = 0.5, size = 30),
        strip.text.x = element_text(size = 25),
        axis.text = element_text(size = 20),
        axis.title = element_text(size = 25))

dev.off()

ggplot(datasetMean, aes(x = cultivar, y = vi, fill=factor(rate)))+
  geom_bar(stat="identity", width = 0.6, position = "dodge", col = "black")+
  scale_fill_discrete(name = "Rate", labels = c("0X","1X","4X","8X"))+
  xlab("Cultivar") + ylab("vi")+
  ggtitle("VI Scores")+
  theme(plot.title = element_text(hjust = 0.5, size = 30),
        strip.text.x = element_text(size = 25),
        axis.text = element_text(size = 20),
        axis.title = element_text(size = 25),
        legend.key.size = unit(1.5, "cm"),
        legend.text = element_text(size = 15),
        legend.title = element_text(size = 20),
        axis.title.y = element_text(angle = 0))