r - Wilcoxon rank sum results: same pvalue over and over? -

i'm comparing pairs of column data wilcoxon rank sum test , getting exact same pvalue majority of comparisons. wondering if judging data whether made mistake or alright. here of comparisons.

this comparison used

wtresult<-wilcox.test(datachunk[,i],datachunk[,(i+1)],paired=false) 

and here results data used above it.

x1     x2     x3                       339.53 354.11 435.56 425.34 434.64 436.08   x1    x2    x3                    312.1 282.2 281.6    na    na    na   wilcoxon rank sum test  data:  datachunk[, i] , datachunk[, (i + 1)] w = 18, p-value = 0.02381 alternative hypothesis: true location shift not equal 0  x1     x2     x3                       161.21 150.01 183.47 201.51 234.70 321.00  x1    x2    x3                    501.0 520.1 500.7    na    na    na   wilcoxon rank sum test  data:  datachunk[, i] , datachunk[, (i + 1)] w = 0, p-value = 0.02381 alternative hypothesis: true location shift not equal 0  x1     x2     x3                       247.79 159.64 192.00 262.86 403.33 336.21  x1    x2    x3                    60.33 66.04 55.23    na    na    na   wilcoxon rank sum test  data:  datachunk[, i] , datachunk[, (i + 1)]  w = 18, p-value = 0.02381 alternative hypothesis: true location shift not equal 0  x1    x2    x3                    17.12 15.83 16.88 17.61 18.97 45.92  x1    x2    x3                    321.8 329.7 334.4    na    na    na  

the test little "chunky" small numbers of observations if have boundary case (all of first argument values larger second argument values or vise versa) identical p-values , w statistics 0 or other number (depending on n).

for more detailed answer we'd need see data or need agree @ other data can see.

here's example of code shows behavior i'm talking about

i <- 1 datachunk <- mtcars[1:5,] wilcox.test(datachunk[,i],datachunk[,(i+1)],paired=false)  <- 2 wilcox.test(datachunk[,i],datachunk[,(i+1)],paired=false)