python - 在Python中获取列表的每个子列表的第一项

Question

我有以下字符串，它是列表的列表:

"ID":[[310.5,1.1612828],[310.0,15.0],[310.0,2.9755309],[309.5,30.0]]

我想将每个列表的所有第一个值抓取到一个变量中，所以在这种情况下输出应该是

print variable

预期输出:

310.5
310.0
310.0
309.5

Answer 1

id = [[310.5,1.1612828],[310.0,15.0],[310.0,2.9755309],[309.5,30.0]]

# If you just want to output to console:
[print(x[0]) for x in id]  #if id a list
# if id is in dict named dict_
[print(x[0] for x in dict_['id']

这是一个更长的版本。

dict_ = {'id': [[310.5,1.1612828],
                [310.0,15.0],
                [310.0,2.9755309],
                [309.5,30.0]]
                }



#make a list containing position 0 values of sublists
pos_0 = [x[0] for x in dict_['id']]
print(pos_0)

#output them to a file
for entry in pos_0:
      print(entry)