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本文實(shí)例講述了python關(guān)于矩陣重復(fù)賦值覆蓋問題的解決方法。分享給大家供大家參考,具體如下:
import itertools import numpy as np comb = list(itertools.combinations(list(range(regions)), 2)) bands_info = [] coeff = np.zeros([bands, len(comb)]) for cla in range(classes): class_info = data[:,cla*bands*regions:(cla+1)*bands*regions] for bs in range(bands): n = bs*regions for i in range(len(comb)): index1 = comb[i][0]+n index2 = comb[i][1]+n part1 = class_info[:, index1] part2 = class_info[:, index2] coeff[bs, i] = (np.corrcoef(part1, part2))[0, 1] bands_info.append(coeff.reshape([1,-1])) coeff_info = np.vstack((bands_info[0], bands_info[1], bands_info[2],bands_info[3]))
例如這個(gè)循環(huán)賦值過程,最終得出來的結(jié)果是bands_info這個(gè)List里面每一個(gè)矩陣都是一樣的,這是為什么呢?我一開始也在這里糾結(jié)了很長(zhǎng)時(shí)間,思來想去感覺沒錯(cuò)的呀。后來想想以前學(xué)的C語言知識(shí),才有點(diǎn)明白。原來python里面有淺層copy和深層copy這一說,同是一個(gè)矩陣的話占用的是同一個(gè)地址,在里面進(jìn)行重復(fù)賦值的話前面的值都會(huì)被覆蓋掉。不只是當(dāng)前變量被覆蓋掉,就是你之后用到這個(gè)變量的也會(huì)被覆蓋。比如說你a的變量被b覆蓋了,那你后面用到a的變量的地方,a的值也會(huì)變成b的值。是不是很可怕。
那么應(yīng)該怎么進(jìn)行修改呢?
import itertools import numpy as np comb = list(itertools.combinations(list(range(regions)), 2)) bands_info = [] for cla in range(classes): coeff = np.zeros([bands, len(comb)]) class_info = data[:,cla*bands*regions:(cla+1)*bands*regions] for bs in range(bands): n = bs*regions for i in range(len(comb)): index1 = comb[i][0]+n index2 = comb[i][1]+n part1 = class_info[:, index1] part2 = class_info[:, index2] coeff[bs, i] = (np.corrcoef(part1, part2))[0, 1] bands_info.append(coeff.reshape([1,-1])) coeff_info = np.vstack((bands_info[0], bands_info[1], bands_info[2],bands_info[3]))
改成這樣就可以了。就是將初始矩陣在循環(huán)里在重新設(shè)定一遍,意思相當(dāng)就是給了一次新的地址,再進(jìn)行復(fù)制的話就不會(huì)覆蓋前面的結(jié)果了。
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