I have a matrix of expression values with the rows as probeIDs and the columns as sample names. I have an associated annotation file with each row corresponding to the row in the expression matrix. Some of the probe IDs share clone IDs. What I would like to do is for the probes that share the same clone IDs I would like to find the median and replace the values in the matrix with the result. Does anyone know the most efficient way of doing this? Many thanks -- ************************************************************** Daniel Brewer, Ph.D. Institute of Cancer Research United Kingdom Email: daniel.brewer at icr.ac.uk ************************************************************** The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company Limited by Guarantee, Registered in England under Company No. 534147 with its Registered Office at 123 Old Brompton Road, London SW7 3RP. This e-mail message is confidential and for use by the addre...{{dropped}}

On Friday 30 March 2007 06:51, Daniel Brewer wrote: > I have a matrix of expression values with the rows as probeIDs and the > columns as sample names. I have an associated annotation file with each > row corresponding to the row in the expression matrix. Some of the > probe IDs share clone IDs. What I would like to do is for the probes > that share the same clone IDs I would like to find the median and > replace the values in the matrix with the result. > > Does anyone know the most efficient way of doing this? The aggregate() function is for doing this type of thing. Sean