A tem o seguinte tagarelice:

structure(list(age = c("21", "17", "32", "29", "15"), 
               gender = structure(c(2L, 1L, 1L, 2L, 2L), .Label = c("Female", "Male"), class = "factor")), 
          row.names = c(NA, -5L), class = c("tbl_df", "tbl", "data.frame"), .Names = c("age", "gender"))

    age gender
  <chr> <fctr>
1    21   Male
2    17 Female
3    32 Female
4    29   Male
5    15   Male

E eu estou tentando usartidyr::spread Para alcançar isto:

  Female Male
1    NA     21
2    17     NA
3    32     NA
4    NA     29
5    NA     15

eu penseispread(gender, age) funcionaria, mas recebo uma mensagem de erro dizendo:

Error: Duplicate identifiers for rows (2, 3), (1, 4, 5)