1. The functions you need to use

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openr, 1, route ——》1 It refers to the memory address of the file under this path

Variable = file_lines( route )——》 The path where the incoming file is located , Return the number of lines of the file

readf, Substitute for , Variables receiving data ——》 The first parameter is a substitute for the memory address of the file , The second is the variable that receives the data

skip_lun, Substitute for , Row number , /lines——》 Specify the nickname of the file , Specify the number of lines to skip , /lines Indicates that the line skipped before

free_lun, 1 Substitute for ——》 Specify the nickname of the file , Memory usage for closing files

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2. Programming

pro week_six_study1
  ;  How to read text data ( Mainly read txt、csv Suffix text file )(txt Are separated by spaces ,csv Are separated by half width commas )
  
  ;  route 
  file_path = 'D:/IDL_program/experiment_data/chapter_4/2013_year_aop.txt'
  
  ;  Xiaobai reads txt file 
  ;  Open the txt file ——》 If you just read the file openr That's all right. ,openw You can read or write ( Will overwrite the original file , Use with caution )
  openr, 1, file_path  ;  first 1 Used to represent the memory address of this file , The second is the path of the file 
  ;  Because the first row is the index , The index is text , Below the index are numbers ,  The two types are inconsistent , It cannot be stored in an array , So we need to skip 
  skip_lun, 1, 1, /lines  ;  first 1 It refers to the number of the file or the memory address , the second 1 Indicates the number of lines to skip , Only the first line is skipped here , So it is 1, The third indicates that the unit of the second parameter is row, not column 
  ;  Create a stored array 
  box_data = fltarr(5, 56304)  ;  Open the file through notepad and check the number of rows and columns of the data in the file in advance ( share 5 Column 56305 That's ok , But skip the first line, so just 56304 That's ok )
  ;  Get the data of the file 
  readf, 1, box_data
  ;  Check it out. 
  print, box_data[0, -1]  ;  Find a new thing is idl The value of can also be negative ( and python equally , I don't know ), This is equivalent to box_data[0, 56303]
  ;  Close file ( Develop good habits )
  free_lun, 1
  
  ;  Normal people read txt file 
  ;  Open the txt file 
  openr, 1, file_path  ;  If you don't have free_lun,1 Then it can't be opened here 
  ;  Get the index data in the first row , This is also useful ( Get the number of columns ), Skipping seems a little wasteful 
  ;  There is one in advance str Variables store 
  str = ''
  readf, 1, str  ;  Here you may wonder , But what? ？readf It's about giving as much as you have , Now? str Is a string , The default output is one line , If you are an array , Then, according to the number of rows and columns of the array, give as many 
  ;  For the obtained data with the first row of index stored str Variables for analysis , Analyze how many columns the whole data has through this string 
  son_str_array = strsplit(str, /extract)  ;  Do not pass in what is the separator , By default, space is used as the separator of the string 
  ; son_str_array There are several elements in it , Then the whole data has several columns 
  column = n_elements(son_str_array)
  ;  Now get the number of rows 
  row = file_lines(file_path) - 1  ;  The first line is the index , We won't put it in the following array 
  ;  Create a stored array 
  box_data = fltarr(column, row)
  ;  get data （ The number of lines obtained here starts from the beginning of the second line , Because it's already readf, 1, str 了 , So the file pointer has pointed to the beginning of the second line ）
  readf, 1, box_data
  ;  Check it out. 
  print, box_data[0, -1]
  ;  Close file 
  free_lun, 1
  
  ;  Master read txt file 
  ;  Open file 
  openr, 1, file_path
  ;  Skip the first line 
  skip_lun, 1, 1, /lines
  ;  The number of lines to read from the file 
  row = file_lines(file_path) - 1
  ;  Create a stored list 
  box_data = fltarr(5, row)  ;  there 5 It's through txt Open notepad and see 
  ;  obtain txt File data 
  readf, 1, box_data
  ;  Check it out. 
  print, box_data[0, -1]
  ;  Close file 
  free_lun, 1
  ;  Maybe you'll ask , What's the advanced , I want to say , Advanced is not everything that needs programming , Efficiency is the most important 
  ;  In this document , We know that the number of columns generally does not change , So why not open it directly with Notepad , But the number of lines is different for each file 
  ;  It's ok if it's a file , If there are many documents , Do you open it with Notepad , It's unrealistic , I won't talk about more .
  
  ;  Read csv file 
  ;  route 
  file_path = 'D:/IDL_program/experiment_data/chapter_4/air_quality_data.csv'
  ;  Read the file 
  data = read_csv(file_path, header=par_name)  ;  The index of the first row is given to the data par_name( But whether you need the first row of index data or not ,read_csv() The function will not read the data in the first row by default )
  ;  see data The type of 
  help, data  ;  You can find , This is a structure 
  ;  Output the first column of data 
  print, data.(0)
  ;  Output the index data of the first row 
  print, par_name
  ;  The output column index is NO2 The data of ( In the first method, you can count the column number by yourself, read it and output it in the above way , You can also use the following method )
  NO2_index = where(par_name eq 'NO2')
  print, data.(NO2_index)
end

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I am fried eggplant , Thank you. ！！