I have a table looks like:
date item_id store_id sale_num
1/1/15 33 1 10
1/1/15 33 2 12
1/1/15 33 3 15
1/1/15 44 1 54
1/1/15 44 3 66
1/2/15 33 1 14
....
I want to cast the table, in order to put store_id into multiple columns, and value is the sale_num. The table should be like:
date item_id store1 store2 store3
1/1/15 33 10 12 15
1/1/15 44 54 NA 66
1/2/15 33 14 NA NA
......
When I do this using cast function in a small scale, 1000 rows in original table, there is no problem.
However, the original table has 38,000,000 rows and comsumes 1.5 GB memory in R. When I use cast function, the function cost around 34 GB memory, and it runs endlessly.
What is the problem of it? Is there any alternative way?