Hi, May be I misunderstood ur question. The output David got could be also obtained by: #df1 dataset
library(plyr) df2<-ddply(df1,.(cat),function(x) if(min(table(x$name))>1){x1<- t.test(val~name,x);cbind(t=x1$statistic,p.value=x1$p.value)}) df2 # cat t p.value #1 p178266580 -0.1156475 0.9144054453 #2 p178316310 -1.0874356 0.4143944591 #3 p191287337 -0.6776053 0.5315717871 #4 p195158904 1.1522850 0.2769290728 #5 p196921846 -4.2342996 0.0003925339 But, the second part is still unclear. A.K. ----- Original Message ----- From: David Carlson <dcarl...@tamu.edu> To: 'Nico Met' <nicome...@gmail.com>; 'R help' <r-help@r-project.org> Cc: Sent: Monday, July 15, 2013 1:33 PM Subject: Re: [R] t-test across columns This may be close to what you want: > t.val <- by(x, x$cat, function(y) if (min(table(y$name)>1)) { + t.test(val~name, y)}) > t.out <- do.call(rbind, sapply(t.val, function(y) c(y$statistic, + p.value=y$p.value))) > t.out t p.value p178266580 -0.1156475 0.9144054453 p178316310 -1.0874356 0.4143944591 p191287337 -0.6776053 0.5315717871 p195158904 1.1522850 0.2769290728 p196921846 -4.2342996 0.0003925339 But I'm not sure what you mean about columns for each cat unless you want the frequencies: > freq.out <- xtabs(~cat+name, x) > freq.out <- freq.out[apply(freq.out, 1, function(y) min(y) > 1),] > freq.out name cat 12.2 15.9 p178266580 4 11 p178316310 2 3 p191287337 3 5 p195158904 8 7 p196921846 26 5 > results <- cbind(freq.out, t.out) > results 12.2 15.9 t p.value p178266580 4 11 -0.1156475 0.9144054453 p178316310 2 3 -1.0874356 0.4143944591 p191287337 3 5 -0.6776053 0.5315717871 p195158904 8 7 1.1522850 0.2769290728 p196921846 26 5 -4.2342996 0.0003925339 ------------------------------------- David L Carlson Associate Professor of Anthropology Texas A&M University College Station, TX 77840-4352 -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Nico Met Sent: Monday, July 15, 2013 10:50 AM To: R help Subject: [R] t-test across columns Dear all, I would like to do t-test across two columns "name" with different "cat" with overall mean ("val"). (Removing if there is a single observation) And finally, make a matrix with t-value and p-value associated with a name (in rows) and cat (in columns) dput(x) structure(list(name = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("12.2", "15.9" ), class = "factor"), cat = structure(c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 3L, 1L, 3L, 3L, 3L, 3L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 5L, 6L, 6L, 6L, 6L, 6L, 6L, 6L), .Label = c("p178266580", "p178269196", "p178316310", "p191287337", "p195158904", "p196921846", "p197427158", "p238921966"), class = "factor"), val = c(148.90772, 184.253375, 183.974866666667, 191.868125, 173.30515, 187.876975, 177.453775, 184.799525, 212.39065, 205.504525, 186.152025, 194.337075, 193.2703, 204.71665, 211.4452, 202.609175, 203.72918, 193.7261, 196.1186, 202.79556, 203.48818, 191.13744, 205.23315, 198.66842, 196.81032, 200.90512, 206.13564, 205.372225, 196.22835, 211.04686, 219.977133333333, 224.7602, 231.6596, 211.105816666667, 215.44474, 210.83514, 228.173125, 224.09034, 212.96026, 239.0085, 213.5407, 227.12115, 209.24888, 232.8964, 232.22146, 228.1643, 236.43082, 232.20792, 238.49192, 224.64014, 233.75898, 207.06138, 215.3649, 211.14802, 201.86854, 200.52278, 199.05752, 194.90904, 214.44334, 249.357266666667, 239.98525, 234.508483333333, 243.865083333333, 233.595816666667, 248.1219, 225.289416666667, 248.220883333333, 193.69566, 198.43578, 205.06055, 208.525975, 198.28692, 206.88496, 201.60162, 205.7943, 210.5117, 196.69886, 193.58288, 198.86094, 201.81676, 225.8266, 205.879725, 218.370475, 214.006125, 198.74038, 206.00314, 198.37446, 225.5357, 216.721025, 226.543925, 158.1011, 158.15674, 166.07518, 179.942225, 158.16046, 165.0685, 159.56146 )), .Names = c("name", "cat", "val"), class = "data.frame", row.names = c( NA, 97L)) Thanks Nico [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.