Hi All - Please see below and advise if you would know the cause for the error "invalid 'z' argument". I have ensured z is the same dimension as 'x', and 'y'. Thanks much.> unique(sort(returns$ABC)) [1] 3.797441 3.799774 3.803247 3.810240 3.813741 3.816694 3.817892 3.830253 [9] 3.831925 3.834632 3.840804 3.840918 3.844687 3.845418 3.846447 3.847197 [17] 3.847941 3.847959 3.850835 3.853354 3.853437 3.855340 3.857322 3.859312 [25] 3.859436 3.859784 3.861996 3.863260 3.865748 3.893238 3.899964 3.901930 [33] 3.904342 3.914072 3.918178 3.920001 3.923059 3.928393 3.928587 3.929148 [41] 3.936047 3.937208 3.939532 3.939833 3.940528 3.944839 3.945068 3.958581 [49] 3.962122 3.962215 3.963068 3.963242 3.968346 3.968727 3.969420 3.969672 [57] 3.976058 3.977803 3.978424 3.980592 3.981944 3.998648 4.028175 4.035569 [65] 4.038265 4.041785 4.042338 4.050577 4.051642 4.051682 4.052925 4.054387 [73] 4.055002 4.055685 4.060776 4.061649 4.063652 4.065851 4.066597 4.066776 [81] 4.068439 4.076675 4.083155 4.083182 4.083943 4.086031 4.090011 4.090803 [89] 4.092659 4.094053 4.097773 4.098674 4.099444 4.102895 4.105761 4.105940 [97] 4.107467 4.108816 4.111324 4.112365 4.112706 4.114066 4.115887 4.119281[105] 4.120303 4.120353 4.122410 4.126879 4.128161 4.133401 4.133904 4.134200[113] 4.135030 4.135330 4.137343 4.137464 4.138053 4.139010 4.146901 4.151760[121] 4.151934 4.152196 4.152219 4.155420 4.156279 4.161443 4.163809 4.171010[129] 4.285857 4.286890 4.288882 4.297404 4.302733 4.303441 4.304059 4.309363[137] 4.312870 4.314272 4.332501 4.339840> unique(sort(returns$DEF)) [1] 8.009089 8.014559 8.014727 8.017862 8.022953 8.023444 8.025575 8.026716 [9] 8.027040 8.034358 8.039206 8.046752 8.052659 8.054409 8.056153 8.058215 [17] 8.058844 8.059320 8.060425 8.060584 8.062793 8.063419 8.064991 8.065621 [25] 8.065769 8.065937 8.067031 8.068444 8.072508 8.094253 8.100334 8.102010 [33] 8.105487 8.108199 8.108348 8.109252 8.111648 8.115245 8.116593 8.117635 [41] 8.120910 8.126098 8.127130 8.128163 8.129635 8.134924 8.138145 8.138726 [49] 8.141204 8.141785 8.142517 8.145413 8.146001 8.149181 8.150048 8.152786 [57] 8.152934 8.153076 8.153365 8.154800 8.168210 8.171458 8.197119 8.213510 [65] 8.220072 8.221470 8.221874 8.223082 8.223568 8.224290 8.225093 8.225492 [73] 8.226834 8.228704 8.228970 8.229236 8.229498 8.229581 8.230040 8.233762 [81] 8.235433 8.240106 8.243349 8.243611 8.245108 8.248517 8.250297 8.251915 [89] 8.257835 8.258229 8.260551 8.264551 8.269173 8.269175 8.269940 8.271095 [97] 8.272504 8.272882 8.274036 8.276201 8.276372 8.277342 8.279374 8.281900[105] 8.284558 8.285869 8.286325 8.286575 8.286705 8.288210 8.288712 8.289339[113] 8.290465 8.290970 8.292476 8.294727 8.295974 8.298833 8.301820 8.302554[121] 8.310582 8.311779 8.311938 8.312800 8.315490 8.316712 8.317445 8.334876[129] 8.432085 8.434150 8.438700 8.439027 8.441080 8.443663 8.445809 8.446354[137] 8.448713 8.456289 8.459144 8.477729> unique(sort(returns$GHI)) [1] 4.252273 4.253354 4.254225 4.258427 4.259970 4.260334 4.261348 4.261840 [9] 4.262250 4.263915 4.265389 4.267696 4.272864 4.276541 4.278934 4.279932 [17] 4.280805 4.282451 4.283374 4.284114 4.284232 4.284401 4.285025 4.285034 [25] 4.286470 4.287052 4.287411 4.288451 4.288782 4.295856 4.296923 4.297826 [33] 4.298914 4.301299 4.302888 4.302934 4.305027 4.305103 4.305802 4.306633 [41] 4.306773 4.307109 4.307745 4.308052 4.308992 4.310062 4.310210 4.310234 [49] 4.312447 4.312891 4.313355 4.314544 4.315325 4.317847 4.317858 4.320886 [57] 4.325496 4.325505 4.325515 4.330970 4.332286 4.338788 4.339169 4.339795 [65] 4.340624 4.341108 4.341692 4.342570 4.347050 4.349598 4.350190 4.352142 [73] 4.354690 4.358524 4.363928 4.366002 4.367096 4.369419 4.369507 4.370167 [81] 4.370409 4.370785 4.371043 4.371541 4.373860 4.374132 4.374649 4.374676 [89] 4.376530 4.378135 4.378297 4.378880 4.379412 4.379581 4.379779 4.380229 [97] 4.381423 4.384481 4.385149 4.385688 4.386779 4.387584 4.388770 4.388847[105] 4.390346 4.391268 4.392438 4.392960 4.393703 4.395858 4.396519 4.397127[113] 4.398971 4.399631 4.401002 4.404109 4.404298 4.404493 4.408388 4.408774[121] 4.410844 4.413465 4.415812 4.418293 4.420801 4.427057 4.430180 4.433600[129] 4.434509 4.438002 4.441285 4.441857 4.443790 4.446019 4.452260 4.458230[137] 4.459305 4.465445 4.469132 4.472145> persp(x=unique(sort(returns$ABC)), y=unique(sort(returns$DEF)), z=((returns$GHI)), xlab="ABC", ylab="DEF", zlab="GHI")Error in persp.default(x = unique(sort(returns$ABC)), y = unique(sort(returns$DEF)), : invalid 'z' argument> persp(x=unique(sort(returns$ABC)), y=unique(sort(returns$DEF)), z=(unique(sort(returns$GHI))), xlab="ABC", ylab="DEF", zlab="GHI")Error in persp.default(x = unique(sort(returns$ABC)), y = unique(sort(returns$DEF)), : invalid 'z' argument

The default use of persp is having x and y as the axis and z as a matrix reflecting the values of the surface/contour. e.g:R> x <- 1:10R> y <- 1:10R> z <- outer(x,y,function(a,b) a*b)R> persp(x=x,y=y,z=z)Which isn't actually related to what you seem to be doing, so the question I'd raise is what do you want to do rather than what do you want persp to do?

Thanks Hansi. All I had wanted to do was what persp was designed to do. Your explanation has cleared it up - thanks.