用于遍历dataframe和data.table列名称

问题描述

我有两个几乎相同的对象，其中一个是数据框，另一个是data.table。我想遍历两个列，并在数据框的列上运行索引。这是我的代码。

library(data.table)

df_1 <- data.frame(col_1 = c(1,2),col_2 = c(3,4))
df_2 <- as.data.table((df_1))

for (el in colnames(df_1)){
  print(df_1[el])
  print(df_2[el])
}

它失败并显示错误：

Error in `[.data.table`(df_2,el) : 
  When i is a data.table (or character vector),the columns to join by must be specified using 'on=' argument (see ?data.table),by keying x (i.e. sorted,and,marked as sorted,see ?setkey),or by sharing column names between x and i (i.e.,a natural join). Keyed joins might have further speed benefits on very large data due to x being sorted in RAM.

我也尝试过：

for (el in seq_along(colnames(df_1))){
  print(el)
  print(df_1[el])
  print(df_2[,el])
}

这是错误消息：

Error in `[.data.table`(df_2,el) : 
  j (the 2nd argument inside [...]) is a single symbol but column name 'el' is not found. Perhaps you intended DT[,..el]. This difference to data.frame is deliberate and explained in FAQ 1.1.

有什么想法吗？

解决方法

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