My output looks like this for z values of the mpg column:
[1] 0.15088482 0.15088482 0.44954345 0.21725341 -0.23073453 -0.33028740
[7] -0.96078893 0.71501778 0.44954345 -0.14777380 -0.38006384 -0.61235388
[13] -0.46302456 -0.81145962 -1.60788262 -1.60788262 -0.89442035 2.04238943
[19] 1.71054652 2.29127162 0.23384555 -0.76168319 -0.81145962 -1.12671039
[25] -0.14777380 1.19619000 0.98049211 1.71054652 -0.71190675 -0.06481307
[31] -0.84464392 0.21725341
Show us the commands you used and the resulting output.