R how to remove duplicates elements in the column and get average value

Question

Sorry I am new to R, and the problem is quite hard for me,
Here is the matrix:

        V1              predictions
1   Jeffery Howes   0.0909596345057677
2   Sherilee Waring 0.00434589236424605
3   Rachel Maitland 0.0909596345057677
4   Jan Maitland    0.0909596345057677
5   Jan Maitland    0.0909596345057677
6   Jan Maitland    0.0909596345057677
7   Jan Maitland    0.0909596345057677
8   Sandra McEwen   0.0909596345057677
....

How can I remove the duplicates in the columns (that's okay for me, could use unique, but the following problem is quite hard for me).

For example, there are many duplicated name Jan Maitland, duplicates should be removed, but the predications values should be calculated (the final result left should be the average value of those duplicate names)

Could someone help me on that? thanks a lot!!

See this post: [data.frame Group By column](http://stackoverflow.com/questions/18799901/data-frame-group-by-column) — zx8754, May 19 '14 at 13:44

droopy · Accepted Answer · 2014-05-19T14:00:10.983

1

you can use the dplyr library :

result%.%group_by(V1)%.%summarise(predictions = mean(predictions))
# the 2nd syntax
summarise(group_by(result, V1), predictions=mean(predictions))

hth

edited May 19 '14 at 14:00

answered May 19 '14 at 13:42

droopy

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thanks! what's the meaning of tab? forget to mention that the matrix name is result, so it should be result%.%group_by(V1)%.%summarise(predictions = mean(predictions))?? – Jusleong May 19 '14 at 13:47
Hi droppy, not quite understand the %.% – Jusleong May 19 '14 at 13:56
yes it should be result instead of tab and result must be a data.frame and a not a matrix; I'll edited the post – droopy May 19 '14 at 13:59
thanks! btw, how should I convert matrix to data.frame – Jusleong May 19 '14 at 14:02
as.data.frame(result)? – Jusleong May 19 '14 at 14:02
yes but first are you sure that result is a matrix? – droopy May 19 '14 at 14:31

R how to remove duplicates elements in the column and get average value

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