[英]Python ignoring command to remove items from list
我正在篩選大量詞典。 kept
是全局列表,其中包含大約9000個字典,所有字典都具有相同的鍵。 我正在嘗試刪除所有'M_P'值大於-4.5的字典,並且其中一半以上,因此我僅為他的目的創建了一個函數。 當我檢查一下是否在以后的功能中將它們全部刪除時,仍然還有〜3000。 誰能告訴我為什么會發生這種情況,我是否可以相信這些功能將按照我的指示去做?
def removeMag():
countMag = 0
for mag in kept:
if to_float(mag['M_P']) > -4.5:
kept.remove(mag)
countMag += 1
else:
continue
print '\n'
print ' Number of mags > -4.5 actually removed: '
print countMag
def remove_anomalies():
count = 0
count08 = 0
count09 = 0
count01 = 0
countMag = 0
countMagDim = 0
#Want to remove Q* < 15 degrees
for row in kept:
#to_float(kept(row))
#Q* greater than 15
if to_float(row['Q*']) < 15.00:
kept.remove(row)
elif to_float(row['vel']) > 80.00:
kept.remove(row)
elif to_float(row['err']) >= 0.5*to_float(row['vel']):
kept.remove(row)
elif row['log_10_m'] == '?':
kept.remove(row)
#print row
count+=1
elif row['M_P'] == '?':
kept.remove(row)
countMag += 1
elif to_float(row['M_P']) > -4.5:
countMagDim += 1
就在這里,我正在檢查它。 ^^^
elif to_float(row['T_j']) < -50.00 or to_float(row['T_j'] > 50.00):
kept.remove(row)
count01 += 1
#make sure beg height is above end height.
elif to_float(row['H_beg']) < to_float(row['H_end']):
kept.remove(row)
#make sure zenith distance is not greater than 90
elif to_float(row['eta_p']) > 90.00:
kept.remove(row)
#Remove extremities hyperbolic orbits
elif (to_float(row['e']) > 2.00 and to_float(row['e']) == 0.00 and to_float(row['a']) == 0.00 and to_float(row['incl']) == 0.00 and to_float(row['omega']) == 0.00 and to_float(row['anode']) == 0.00 and to_float(row['alp_g']) == 0.00 and to_float(row['del_g']) == 0.00 and to_float(row['lam_g']) == 0.00 and to_float(row['bet_g']) == 0.00):
kept.remove(row)
count08+=1
elif to_float(row['q_per']) == 0.00:
kept.remove(row)
count09+=1
elif to_float(row['q_aph']) == 0.00:
kept.remove(row)
count09+=1
else: continue
print 'Number of dicts with ? as mass value:'
print count
print " Number removed with orbital elements condition: "
print count08
print "Number of per or aph equal to 0: "
print count09
print "Number of T_j anomalies: "
print count01
print "Number of Magnitudes removed from '?': "
print countMag
以下輸出類似3000。
print "Number of Magnitudes to be removed from too dim: "
print countMagDim
'''
print "\n"
print "log mass values:"
for row2 in kept:
print row2['log_10_mass']
print "\n"
'''
使用for循環進行迭代時,Python不會自動創建列表的副本,而是直接對其進行迭代。 因此,當您刪除一個元素時,循環將不會考慮更改,並且會跳過列表中的元素。
例:
>>> l = [1,2,3,4,5]
>>> for i in l: l.remove(i)
>>> l
[2, 4]
您可以使用列表索引作為速記,以在迭代之前制作列表的副本,例如:
>>> for i in l[:]: l.remove(i)
>>> l
[]
正如其他人所說,您在迭代數組時正在修改它。
一個簡單的單線是
kept = [mag for mag in kept if to_float(mag['M_P']) <= -4.5]
只需保留您感興趣的所有條目,即可替換原始列表。
計算除去的數量僅是在理解前后取len(kept)
並取其差值即可。
或者,
discarded = [mag for mag in kept if to_float(mag['M_P']) > -4.5]
kept = [mag for mag in kept if to_float(mag['M_P']) <= -4.5]
拆分數組而不會丟失任何信息
您永遠不要修改for循環中要迭代的序列。 看一下您的第一個功能:
def removeMag():
countMag = 0
for mag in kept:
if to_float(mag['M_P']) > -4.5:
kept.remove(mag)
countMag += 1
您正在呼吁remove
關於kept
在環。 這會導致未指定的行為,並且可能發生任何事情。 看到這個問題 。
解決此問題的一種簡單方法是對要保留的項目使用新列表:
mag_to_keep = []
for mag in kept:
if float(mag['M_P']) <= -4.5:
mag_to_keep.append(mag)
kept = mag_to_keep
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