JohnnyDeer - 2 months ago 6

R Question

I am trying to merge values in a dataframe by every nth row.

The data structure looks as follows:

`id value`

1 1

2 2

3 1

4 2

5 3

6 4

7 1

8 2

9 4

10 4

11 2

12 1

I like to aggregate the values for every 4 rows each. Actually, the dataset describes a measurement for each a 4-day period. id"1"=day1, id"2"=day2, id"3"=day3, id"4"=day4, id"5"=day1,... As such, a column counting in a looĆ¼ from 1 to 4 might be used?

The result should look like (sums):

`day sum`

1 8

2 10

3 4

4 5

Answer

This can be achieved with `%%`

for creating a grouping variable and then do the `sum`

with `aggregate`

```
n <- 4
aggregate(value ~cbind(day = (seq_along(df1$id)-1) %% n + 1), df1, FUN = sum)
# day value
#1 1 8
#2 2 10
#3 3 4
#4 4 5
```

Source (Stackoverflow)

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