Convert R dataframe from long to wide format [duplicate]

Answer 1

The shortest solution is probably using the rowid function from the data.table package:

library(data.table)
dt <- dcast(setDT(df), rowid(left) ~ left, value.var = "right")
dt[, names(dt)[1] := NULL]

which gives:

> dt
    a  b  c  d
1: 18 52 67 12
2: 36 74 61 86
3: 81 41 82  3

Answer 2

Sticking with dplyr and tidyr (appreciate it's not as neat as other answers!):

df %>% 
mutate(rowId = 1:n()) %>%
group_by(rowId) %>% 
spread(left, right) %>% #gives you wide df with NAs
ungroup() %>% 
select(-rowId) %>% 
mutate(temp = rep(1:3, each = 4)) %>% 
group_by(temp) %>% 
summarise_each(funs(mean(., na.rm = TRUE))) %>% 
ungroup() %>% 
select(-temp)