Median on second group of CSV file produce Na

I have a data frame  csv file and I'm trying to calculate median for each
group separately row by row . When I separate the data frame in two groups
and calculate the median for each one, I am getting an NA result for the
second group :
the data
  x1  x2  x3  x4  x5  x6  x7  y1  y2  y3  y4  y5  y6  y7  y8
9.488404158 9.470895414 9.282433728 9.366707445 9.955383045 9.640816474
9.606262272   9.329651027 9.434541611 9.473922432 9.311412966 9.3154885
9.434977488 9.470895414 9.764258059
8.630629966 8.55831075  8.788391003 8.576231135 8.671587906 8.842979993
8.861958856 8.58330436  8.603596508 8.570129609 8.59798922  8.572686772
8.679751791 8.663950953 8.432875347
9.354748885 9.367668838 9.259952558 9.421538213 9.554635162 9.603744578
9.452197983 9.284228877 9.404607878 9.317737979 9.343115301 9.310644266
9.27227486  9.360337823 9.44706281
9.944863964 9.950427516 10.19101759 10.07350804 10.03269879 10.1307908
 10.03487287 9.74609383  9.886379007 9.775472567 10.036596   9.544738458
9.699611598 9.911962567
9.625804277


                                   Code:

       rowN <- nrow(AT1)
       MD1<-vector(length=rowN)
      MD2<-vector(length=rowN)

          MD1[1:rowN]<-NA
          MD2[1:rowN]<-NA


         x<- AT1[,c(2,3,4,5,6,7,8) ]
        write.csv(x,"x.csv",row.names=TRUE)
         x<-as.matrix(x)
        for(i in 2:rowN) {
       MD1[i]=median(x[i,])
          }
         write.csv(MD1,"MD1.csv",row.names=TRUE)

         y<- AT1[,c(9,10,11,12,13,14,15,16)]
         write.csv(y,"y.csv",row.names=TRUE)
         y<-as.matrix(y)
         for(j in 2:rowN) {
         MD2[j]=median(y[j,])
          }
         write.csv(MD2,"MD2.csv",row.names=TRUE)


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