df<-data.frame(stringsAsFactors=FALSE,
Subject = c("Arts", "History", "Maths", "French", "HomeEc"),
student_1 = c(50L, 51L, 52L, 53L, 54L),
student_2 = c(67L, 68L, 69L, 70L, 71L),
student_3 = c(82L, 83L, 84L, 85L, 86L))


   Subject student_1 student_2 student_3
1    Arts        50        67        82
2 History        51        68        83
3   Maths        52        69        84
4  French        53        70        85
5  HomeEc        54        71        86

df2<-data.frame(stringsAsFactors=FALSE,
Subject = c("Arts", "History", "Maths", "Spanish", "Photography"),
student_4 = c(40L, 41L, 42L, 43L, 44L),
student_5 = c(71L, 72L, 73L, 74L, 75L),
student_6 = c(92L, 93L, 94L, 95L, 96L)
)

      Subject student_4 student_5 student_6
1        Arts        40        71        92
2     History        41        72        93
3       Maths        42        73        94
4     Spanish        43        74        95
5 Photography        44        75        96

Subject student_1 student_2 student_3 student_4 student_5 student_6
1        Arts        50        67        82        40        71        92
2     History        51        68        83        41        72        93
3       Maths        52        69        84        42        73        94
4      French        53        70        85        NA        NA        NA
5      HomeEc        54        71        86        NA        NA        NA
6     Spanish        NA        NA        NA        43        74        95
7 Photography        NA        NA        NA        44        75        96