[R] Adding a value to one dataframe from another dataframe

[Nick Duncan]

Dear All
the problem I have is as follows.

I have attribute data in a number of data.frames identified 1:58 (the
column Null is just there to stop it becoming a list, which caused me
trouble, the data I am interested in is in column 1, although other
data frames have multiple categories/cols). The attribute data frames
are always organised with 58 rows.

          ID     Null
1        NA       1
2  86.11111     2
3  88.88889     3
4 100.00000    4
5  80.55556     5
6  97.22222     6

In another data frame I have clusters in which the subjects 1:58
appear in different combinations.

SCD.TD cluster
1      1       4
2      1      17
3      2       4
4      2      13
5      2      17
6      3       4

The ID attribute of 2 is 86.1111 and the subject appears in three
clusters. The data frames have different sizes but with the same
number of subjects (row 1 is always the same subject)
I need to analyse the clusters by the values of a number of
attributes. For example I would like to be able to get descriptive
statistics of attribute ID by cluster. I'd like to have a general
approach if possible.
There are NA's in attribute data frames and should be transferred.

What I need to get to is below

SCD.TD cluster ID
1      1       4   NA
2      1      17   NA
3      2       4    86.11111
4      2      13   86.11111
5      2      17   86.11111
6      3       4    88.88889

>From that point I can treat the cluster as a factor and presumably the
analysis is straightforward from there.

Many thanks in advance for any assistance.

Nick