[R] How to calculate means for multiple variables in samples with different sizes

From: Aline Santos <alinexss_at_gmail.com>
Date: Fri, 11 Mar 2011 10:32:18 +0100


Hello R-helpers:

I have data like this:

sample replicate height weight age

A    1.00    12.0    0.64    6.00
A    2.00    12.2    0.38    6.00
A    3.00    12.4    0.49    6.00
B    1.00    12.7    0.65    4.00
B    2.00    12.8    0.78    5.00
C    1.00    11.9    0.45    6.00
C    2.00    11.84    0.44    2.00
C    3.00    11.43    0.32    3.00
C    4.00    10.24    0.84    4.00
D    1.00    14.2    0.54    2.00
D    2.00    15.67    0.67    7.00
D    3.00    15.11    0.81    7.00

Now, how can I calculate the mean for each condition (heigth, weigth, age) in each sample, considering the samples have different number of replicates?

The final matrix should look like:

sample height weight age
A 12.20 0.50 6.00

B     12.75      0.72      4.50
C     11.35      0.51      3.75
D     14.99      0.67      5.33

This is a simplified version of my dataset, which consist of 100 samples (unequally distributed in 530 replicates) for 600 different conditions.

I appreciate all the help.

A.S.

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