如何将一列数据框保留为数据框

Question

Question: how to extract a column of dataframe and keep its structure as unchanged?

data <- iris
data[, 1] ##this will be a vector and will lose the name of the column in dataframe

Answer 1

data[, 1, drop = FALSE]可以解决问题。

Answer 2

Use list subsetting which will return a data frame:

data[1]

Produces

  Sepal.Length
1          5.1
2          4.9
3          4.7
4          4.6
5          5.0
6          5.4
# ... omitted rows

When you use only one argument to [ with data frames it subsets data frames as lists, where each column is an element. It also preserves attributes, so the subset of the data frame is also a data frame.