创建空数据框

Question

我创建了一个完全空的矩阵。我想在2个索引中分割观察（如在Excel中）。

Indices <- matrix(NA, 8, 2)
rownames(Indices) <- rownames(Indices, do.NULL = FALSE, prefix = "Plot")  # brauche ich das?
rownames(Indices) <- c("Plot 1", "Plot 2", "Plot 3", "Plot 8", "Plot 9", "Plot 10", 
                       "Plot 12", "Plot 13")
colnames(Indices) <- c("Density", "Trees per ha")

我想在Density和Density only Oaks中将Density total分开一次。我不知道如何调用它，这在R？中是否可行？