how to create a list of lists

Question

My Python code generates a list everytime it loops   list   np genfromtxt  temp txt   usecols 3  dtype    floatname   float     skip header 1    But I want to save each one - I need a list of lists right   So I tried   list i    np genfromtxt  temp txt   usecols 3  dtype    floatname   float     skip header 1    But Python now tells me that  list  is not defined  I m not sure how I go about defining it  Also  is a list of lists the same as an array    Thank you

User · Answer

First of all do not use list as a variable name- that is a builtin function   I m not super clear of what you re asking  a little more context would help   but maybe this is helpful-  my list      my list append np genfromtxt  temp txt   usecols 3  dtype    floatname   float     skip header 1   my list append np genfromtxt  temp2 txt   usecols 3  dtype    floatname   float     skip header 1     That will create a list  a type of mutable array in python  called my list with the output of the np getfromtext   method in the first 2 indexes   The first can be referenced with my list 0  and the second with my list 1

User · Answer

You want to create an empty list  then append the created list to it   This will give you the list of lists   Example    gt  gt  gt  l       gt  gt  gt  l append  1 2 3    gt  gt  gt  l append  4 5 6    gt  gt  gt  l   1  2  3    4  5  6

User · Answer

Create your list before your loop  else it will be created at each loop    gt  gt  gt  list1       gt  gt  gt  for i in range 10          list1 append  range i 10         gt  gt  gt  list1   0  1  2  3  4  5  6  7  8  9    1  2  3  4  5  6  7  8  9    2  3  4  5  6  7  8  9    3  4  5  6  7  8  9    4  5  6  7  8  9    5  6  7  8  9    6  7  8  9    7  8  9    8  9    9

User · Answer

Use append method  eg     lst      line   np genfromtxt  temp txt   usecols 3  dtype    floatname   float     skip header 1  lst append line

User · Answer

Just came across the same issue today     In order to create a list of lists you will have firstly to store your data  array  or other type of variable into a list  Then  create a new empty list and append to it the lists that you just created  At the end you should end up with a list of lists   list 1 data 1 tolist   list 2 data 2 tolist   listoflists      listoflists append list 1  listoflists append list 2

[python] how to create a list of lists

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