Import CSV file with mixed data types

Question

I m working with MATLAB for few days and I m having difficulties to import a CSV-file to a matrix   My problem is that my CSV-file contains almost only Strings and some integer values  so that csvread   doesn t work  csvread   only gets along with integer values   How can I store my strings in some kind of a 2-dimensional array to have free access to each element   Here s a sample CSV for my needs   04 abc def ghj klm           Test text 0xFF        asdfhsdf dsafdsag 0x0F0F     The main thing are the empty cells and the texts within the cells  As you see  the structure may vary

User · Answer

In R2013b or later you can use a table    gt  gt  table   readtable  myfile txt   Delimiter       ReadVariableNames  false   gt  gt  table         Var1    Var2     Var3     Var4     Var5        Var6          Var7         Var8      Var9    Var10                                                                                                              4      abc      def      ghj      klm                                             NaN     NaN       NaN                                          Test          text          0xFF       NaN     NaN       NaN                                          asdfhsdf      dsafdsag      0x0F0F     NaN     NaN     Here is more info

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Assuming that the dataset is    -delimited and each line ends with     fid   fopen  sampledata csv    tline   fgetl fid   u sprintf   c  tline   c length u   id findstr u       n length id   data cell 1 n   for I 1 n     if I  1         data 1 I  u 1 id I -1       else         data 1 I  u id I-1  1 id I -1       end end ct 1  while ischar tline      ct ct 1      tline   fgetl fid       u sprintf   c  tline       id findstr u           if isempty id          for I 1 n             if I  1                 data ct I  u 1 id I -1               else                 data ct I  u id I-1  1 id I -1               end         end     end end fclose fid

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Given the sample you posted  this simple code should do the job   fid   fopen  file csv   r    C   textscan fid  repmat   s  1 10    delimiter        CollectOutput  true   C   C 1   fclose fid     Then you could format the columns according to their type  For example if the first column is all integers  we can format it as such   C   1    num2cell  str2double C   1       Similarly  if you wish to convert the 8th column from hex to decimals  you can use HEX2DEC   C   8    cellfun  hex2dec  strrep C   8   0x        UniformOutput  false     The resulting cell array looks as follows   C           4      abc      def      ghj      klm                                                         NaN                                          Test          text           255                   NaN                                          asdfhsdf      dsafdsag      3855

User · Answer

Depending on the format of your file  importdata might work   You can store Strings in a cell array  Type  doc cell  for more information

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If your input file has a fixed amount of columns separated by commas and you know in which columns are the strings it might be best to use the function   textscan     Note that you can specify a format where you read up to a maximum number of characters in the string or until a delimiter  comma  is found

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Have you tried to use the  CSVIMPORT  function found in the file exchange  I haven t tried it myself  but it claims to handle all combinations of text and numbers   http   www mathworks com matlabcentral fileexchange 23573-csvimport

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For the case when you know how many columns of data there will be in your CSV file  one simple call to textscan like Amro suggests will be your best solution   However  if you don t know a priori how many columns are in your file  you can use a more general approach like I did in the following function  I first used the function fgetl to read each line of the file into a cell array  Then I used the function textscan to parse each line into separate strings using a predefined field delimiter and treating the integer fields as strings for now  they can be converted to numeric values later   Here is the resulting code  placed in a function read mixed csv   function lineArray   read mixed csv fileName  delimiter     fid   fopen fileName   r              Open the file   lineArray   cell 100  1               Preallocate a cell array  ideally slightly                                           larger than is needed    lineIndex   1                         Index of cell to place the next line in   nextLine   fgetl fid                  Read the first line from the file   while  isequal nextLine  -1           Loop while not at the end of the file     lineArray lineIndex    nextLine     Add the line to the cell array     lineIndex   lineIndex 1             Increment the line index     nextLine   fgetl fid                Read the next line from the file   end   fclose fid                            Close the file    lineArray   lineArray 1 lineIndex-1                  Remove empty cells  if needed   for iLine   1 lineIndex-1                            Loop over lines     lineData   textscan lineArray iLine     s          Read strings                          Delimiter   delimiter       lineData   lineData 1                              Remove cell encapsulation     if strcmp lineArray iLine  end   delimiter         Account for when the line       lineData end 1                                     ends with a delimiter     end     lineArray iLine  1 numel lineData     lineData     Overwrite line data   end  end   Running this function on the sample file content from the question gives this result    gt  gt  data   read mixed csv  myfile csv         data       Columns 1 through 7       04      abc      def      ghj      klm                                                                               Test          text                                                       asdfhsdf      dsafdsag     Columns 8 through 10                                0xFF                     0x0F0F                The result is a 3-by-10 cell array with one field per cell where missing fields are represented by the empty string     Now you can access each cell or a combination of cells to format them as you like  For example  if you wanted to change the fields in the first column from strings to integer values  you could use the function str2double as follows    gt  gt  data    1    cellfun   s   str2double s    data    1    data       Columns 1 through 7         4      abc      def      ghj      klm                                   NaN                                          Test          text           NaN                                          asdfhsdf      dsafdsag     Columns 8 through 10                                0xFF                     0x0F0F                Note that the empty fields results in NaN values

User · Answer

Use xlsread  it works just as well on  csv files as it does on  xls files  Specify that you want three outputs    num char raw    xlsread  your filename csv     and it will give you an array containing only the numeric data  num   an array containing only the character data  char  and an array that contains all data types in the same format as the  csv layout  raw

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I recommend looking at the dataset array   The dataset array is a data type that ships with Statistics Toolbox  It is specifically designed to store hetrogeneous data in a single container   The Statistics Toolbox demo page contains a couple vidoes that show some of the dataset array features   The first is titled  An Introduction to Dataset Arrays   The second is titled  An Introduction to Joins    http   www mathworks com products statistics demos html

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