For every specific V1 and V4 pair (ex:A and P) calculate Linear regression of V3(y-axis) and V2(x-axis) and print p value along with the pair (output). INPUT ############# V1 V2 V3 V4 A 1 2.5 P A 2 2.8 P A 3 3.2 P A 2 1.1 Q A 3 1.7 Q A 1 2.2 Q B 1 2.5 P B 2 2.9 P B 3 3.0 P SCRIPT ####### data1<-read.table("INPUT", header=TRUE) fm <- lmList(V3~V2|V1,V4 data=data1) get.pval <- function(z) { x <- summary(z) pf(x$fstatistic[1L], x$fstatistic[2L], x$fstatistic[3L], lower.tail = FALSE) } sapply(fm,get.pval) OUTPUT ######## A PVALUE[LINEAR REGRESSION] P A P........................ Q B P........................ P -- View this message in context: http://r.789695.n4.nabble.com/small-change-in-output-tp2068720p2068720.html Sent from the R help mailing list archive at Nabble.com.