Multiply each row by a variable contained within that row to expand the dimensions of the dataframe

Question

I want to multiply each row in a dataframe by X times as defined by a value within the row.

Data:

df <- expand.grid(var1 = 1:3, var2 = 1:3)
df$repeatme = c(2, 3, 11, 6, 14, 1, 7, 8, 30)

The multiplying factor is to be determined by the repeatme variable.

Therefore, I want to multiply :

row 1 ... 2 times (because repeatme == 2);
row 2 ... 3 times (because repeatme == 3);
row 3 ... 11 times (because repeatme == 11);
etc.

Desired Output:

  var1 var2 repeatme
1    1    1        2
2    1    1        2
3    2    1        3
4    2    1        3
5    2    1        3
6    3    1       11
7    3    1       11
8    3    1       11

         ...

EDIT

To be clear, I'm not asking how to multiply variables within rows! I want to alter the structure/dimensions of the dataframe by multiply the rows themselves!

I'm still unclear on what you're asking. Are you sure your data and desired output match up? — ila, Jul 10 '15 at 16:23
there are many duplicates of this question already on SO - saying you want to "duplicate" or "replicate" the rows would be a better search term than "multiply" — Sam Firke, Jul 10 '15 at 16:39

score 2 · Accepted Answer · answered Jul 10 '15 at 16:30

2

df[rep(1:nrow(df), times = df$repeatme), ]

answered Jul 10 '15 at 16:30

jeremycg

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Multiply each row by a variable contained within that row to expand the dimensions of the dataframe

1 Answers1