你可以使用lapply快速地完成这个任务。你并不清楚你到底想要如何合并文件（通过一个公共变量进行真正的合并，或者追加行，或者追加列）。无论哪种方式，我认为你都不需要为as.character做任何改变，下面的任何方法（2A - 2C）都可以工作：

library(readxl)

# 1. Read in all excel files in a folder given a specific filepath
filepath <- "your/file/path/"
file_list <- list.files(path = filepath, pattern='*.xlsx')
df_list <- lapply(file_list, read_excel)

# 2a. Merge data (assuming a unique identifier, i.e "studyid")
final_data <- Reduce(function(...) merge(..., by = "studyid", all = TRUE), df_list)

# 2b. If all files have the same columns, append to one long dataset
final_data <- do.call(rbind, df_list)

# 2c. If you want to make a wide dataset (append all columns)
final_data <- do.call(cbind, df_list)