因此，对于我最近的R类入门课程之一，我们被要求编写一个函数，该函数接受一个向量作为输入，然后通过减去均值并将整个事物除以标准差来更改每个元素。然后，我应该返回这个新向量的标准偏差。 作为一个初学者，我选择创建一个遍历每个元素并执行以下操作的for循环： ``
for(i in 1:length(vec)){
vec[i] <- (vec[i] - mean(vec))/sd(vec)
}
``
但是我得到了错误的输出，最终发现我应该对整个向量本身而不是对每个元素进行运算： ``
vec <- (vec - mean(vec))/sd(vec)
``
两种方法的结果存在实际差异。第一种方法给了我： ``
[1] -1.70622042 -1.66806653 -1.62880198 -1.58852738 -1.54734431 -1.50535419
[7] -1.46265728 -1.41935181 -1.37553311 -1.33129297 -1.28671898 -1.24189407
[13] -1.19689615 -1.15179781 -1.10666616 -1.06156271 -1.01654339 -0.97165858
[19] -0.92695320 -0.88246689 -0.83823422 -0.79428484 -0.75064379 -0.70733173
[25] -0.66436520 -0.62175690 -0.57951591 -0.53764803 -0.49615595 -0.45503952
[31] -0.41429598 -0.37392017 -0.33390472 -0.29424023 -0.25491543 -0.21591735
[37] -0.17723142 -0.13884163 -0.10073057 -0.06287959 -0.02526878 0.01212288
[43] 0.04931753 0.08633842 0.12320983 0.15995716 0.19660684 0.23318646
[49] 0.26972474 0.30625161 0.34279830 0.37939741 0.41608302 0.45289080
[55] 0.48985822 0.52702462 0.56443150 0.60212269 0.64014461 0.67854658
[61] 0.71738116 0.75670451 0.79657685 0.83706297 0.87823279 0.92016207
[67] 0.96293319 1.00663604 1.05136912 1.09724076 1.14437067 1.19289164
[73] 1.24295167 1.29471649 1.34837262 1.40413106 1.46223186 1.52294970
[79] 1.58660093 1.65355232 1.72423224 1.79914503 1.87888958 1.96418394
[85] 2.05589811 2.15509866 2.26311049 2.38160407 2.51272174 2.65926551
[91] 2.82498523 3.01503756 3.23674985 3.50096197 3.82454625 4.23556347
[97] 4.78509150 5.57913167 6.88932519 9.77001045
``
第二种方法给了我： ``
[1] -1.70622042 -1.67175132 -1.63728222 -1.60281312 -1.56834402 -1.53387492
[7] -1.49940582 -1.46493672 -1.43046762 -1.39599852 -1.36152943 -1.32706033
[13] -1.29259123 -1.25812213 -1.22365303 -1.18918393 -1.15471483 -1.12024573
[19] -1.08577663 -1.05130753 -1.01683843 -0.98236933 -0.94790023 -0.91343113
[25] -0.87896203 -0.84449293 -0.81002384 -0.77555474 -0.74108564 -0.70661654
[31] -0.67214744 -0.63767834 -0.60320924 -0.56874014 -0.53427104 -0.49980194
[37] -0.46533284 -0.43086374 -0.39639464 -0.36192554 -0.32745644 -0.29298734
[43] -0.25851825 -0.22404915 -0.18958005 -0.15511095 -0.12064185 -0.08617275
[49] -0.05170365 -0.01723455 0.01723455 0.05170365 0.08617275 0.12064185
[55] 0.15511095 0.18958005 0.22404915 0.25851825 0.29298734 0.32745644
[61] 0.36192554 0.39639464 0.43086374 0.46533284 0.49980194 0.53427104
[67] 0.56874014 0.60320924 0.63767834 0.67214744 0.70661654 0.74108564
[73] 0.77555474 0.81002384 0.84449293 0.87896203 0.91343113 0.94790023
[79] 0.98236933 1.01683843 1.05130753 1.08577663 1.12024573 1.15471483
[85] 1.18918393 1.22365303 1.25812213 1.29259123 1.32706033 1.36152943
[91] 1.39599852 1.43046762 1.46493672 1.49940582 1.53387492 1.56834402
[97] 1.60281312 1.63728222 1.67175132 1.70622042
``
有人可以解释为什么会这样吗？我真的很困惑。