how to apply a function to a data frame in R?-CodePudding

I was wondering how to apply a function to a data frame, for example if I want a function that returns the mean of a certain column (for example column 13 in every data frame I put in the function) how can I specify that instruction and putting the data frame in the place of the argument.

mean <- function (argument) {} 

mean <- function(data frame) {} #this is what I try to do

The thing is that I have to get the average of 13 tables but I only use 1 column of each table and I have to gather them in a single data frame, which I think could be easier if I set a function for each table (data frame) that gives me the unique result.

CodePudding user response：

Treat the input of the function exactly as you would any other dataframe. The below is a general layout of what you are looking for:

df_mean <- function(df) {
    mean(df$desiredColumnName)
}

lapply(dataframe_list, df_mean)

Of course, it assumes that you are looking for the same column name in each dataframe, and that your dataframes are in a list.

Alternatively, as this is quite simple an anonymous function works as well:

lapply(dataframe_list, function(x) mean(x$desiredColumnName))

If you have your files stored as csvs in one directory, you can read them into a list like this:

dataframe_list <- lapply(list.files(directory_path, recursive = TRUE, full.names = TRUE), read.csv)