Creating a pivot table

Question

Suppose I have a dataset that looks like the following, in which years are listed down rows:

id<-c(1,1,1,2,2,2,3,3,3)
year<-c(1990, 1991, 1992, 1992, 1         


        

Answer 1

Another way to do it:

> library(reshape2)
> dcast(dataset, id ~ year, fill=0)
# Using N as value column: use value.var to override.
  id 1990 1991 1992 1993 1994 1995
1  1    7    8    9    0    0    0
2  2    0    0    7    1    2    0
3  3    0    0    0    5    4    3

Answer 2

these days using tidyverse is more the rage:

library(tidyr)

dataset %>% 
  spread(year, N, fill = 0)

Answer 3

> xtabs(N~id+year, data=dataset)
   year
id  1990 1991 1992 1993 1994 1995
  1    7    8    9    0    0    0
  2    0    0    7    1    2    0
  3    0    0    0    5    4    3

Your dataset is in "molten" form using the reshape2 terminology. Also known in data query circles as "first normal form".