R 查找多个数据帧的匹配列名

Question

I have a dataset with various dataframes named "data_t1", "data_t2", ...., "data_t10".

Some of those dataframes share the same variables. Therefore I am trying to find out which variables are shared by each two df.

Instead of comparing the column names of each df with the column names of all the other dataframes manually, i tried to find matching column names by coding a for loop. This is my code so far:

 for (i in 1:10){
      for (j in 1:10){
        assign(paste("common_column_names",toString(i),toString(j),sep="_"), 
           intersect(colnames(noquote(paste("data_t",toString(i),sep=""))), 
                     colnames(noquote(paste("data_t",toString(j),sep="")))))
        }}

Although i know the df share variables, the output keeps being "NULL". The problem seems to be within the colnames() command, because

colnames(noquote(paste("data_t1")))

generates the Output NULL, whereas

colnames(data_t1)

generates a list of the colnames of "data_t1".

I was unable to find a solution for this problem so far.

Thanks.

Answer 1

Here is a one-liner with Reduce . Change the dataframes list name from df_list to your list name and it should work.

Reduce(function(x, y){intersect(x, names(y))}, df_list, init = names(df_list[[1]]))
#[1] "X"

---

Test data creation code

The code below makes sure there is a common column name, "X" and at least one different name in every dataframe, LETTERS[i] .

set.seed(2021)
df_list <- lapply(1:4, function(i){
  df <- data.frame(1:5, 6:10, 11:15)
  names(df) <- c("X", LETTERS[i], sample(LETTERS, 1))
  df
})
names(df_list) <- paste0("data_t", 1:4)