如何将数据帧写入 csv 文件？

Question

I am making a data frame where one column is a major, and the second column is the list of courses in the major.

df <- data.frame(majors = majors) df[,"courses"] <- courses

where majors is a vector and courses is a list of lists. When I try to write using

write.csv(df,"Majors_and_Courses.csv", row.names = FALSE)

I get an error saying "Error in write.table(df, "Majors_and_Courses.csv", row.names = FALSE, : unimplemented type 'list' in 'EncodeElement'"

Answer 1

I suspect that you were creating a data.table or similar, since df[,"courses"] <- courses would otherwise give you a warning.

Solution using data.table:

library(data.table)
dt <- data.table(majors = c("John", "Lisa", "Tim"))
courses <- list(a = list("m","n","o"), b = list("p", "q", "r"), c = list("s", "t", "u"))
dt[,"courses"] <- courses
dt$courses <- vapply(dt$courses, paste, collapse = "; ", character(1L))
write.csv(dt, "Majors_and_Courses.csv", row.names = FALSE)

Unlisting beforehand would change the length, unlisting after adding it to the data table would export the "c(...)" structure. You can change the separator for the nested list the way you wish, but I discourage you to reuse the separator of the file that you are exporting ("," in this case) to avoid confusion.