How to implement 2D vector array

Question

I m using the vector class in the STL library for the first time  How should I add to a specific row of the vector array   struct x       vector  lt vector  lt int gt   gt  v       int row       vector lt  int   gt  my ints  int add    if i wanted to add to first row of v with the first pointer of integers  could I do   myints 0 - gt v myints 0 - gt row  push back add     Is this method fine to create a 2 D vector of vector ints where each row could potentially be of different length  i e  have a different number of columns

User · Answer

I use this piece of code   works fine for me  copy it and run on your computer  you ll understand by yourself     include  lt iostream gt   include  lt vector gt  using namespace std  int main         vector  lt vector  lt int gt   gt  matrix      size t row 3   col 3       for int i 0 cnt 1   i lt row   i                  for int j 0   j lt col   j                          vector  lt int gt  colVector               matrix push back colVector                matrix at i  push back cnt                          matrix at 1  at 1    0        matrix at columns  at rows    intValue        printing all elements     for int i 0 cnt 1   i lt row   i                  for int j 0   j lt col   j                          cout lt  lt matrix i  j   lt  lt                         cout lt  lt endl

User · Answer

Just use the following methods to create a 2-D vector   int rows  columns                     vector  lt  vector  lt  int  gt   gt  Matrix rows  vector lt  int  gt  columns 0      OR    vector  lt  vector  lt  int  gt   gt  Matrix   Matrix assign rows  vector  lt  int  gt  columns  0       Do your stuff here      This will create a Matrix of size rows   columns and initializes it with zeros because we are passing a zero 0  as a second argument in the constructor i e vector  lt  int    columns  0

User · Answer

If you know the  maximum  number of rows and columns beforehand  you can use resize   to initialize a vector of vectors and then modify  and access  elements with operator    Example   int no of cols   5  int no of rows   10  int initial value   0   std  vector lt std  vector lt int gt  gt  matrix  matrix resize no of rows  std  vector lt int gt  no of cols  initial value        Read from matrix  int value   matrix 1  2       Save to matrix  matrix 3  1    5    Another possibility is to use just one vector and split the id in several variables  access like vector  row   columns    column

User · Answer

We can easily use vector as 2d array  We use resize   method for this purpose  The code below can be helpful to understand this issue   Code Snippet     include lt bits stdc   h gt  using namespace std   int main         ios  sync with stdio false       int row  col      cin gt  gt row gt  gt col       vector  lt vector lt int gt  gt  v      v resize col vector lt int gt  row           v     1 2 3    4 5 6    7 8 9              input from use         for int i 0  i lt row  i                 for int j 0  j lt col  j                       cin gt  gt v i  j                       for int i 0 i lt row  i                 for int j 0 j lt col j                       cout lt  lt v i  j  lt  lt                         return 0

User · Answer

vector lt vector gt  matrix row  vector col  0    This will initialize a 2D vector of rows row and columns   col with all initial values as 0  No need to initialize and use resize  Since the vector is initialized with size  you can use  quot    quot  operator as in array to modify the vector  matrix x  y    2

User · Answer

I m not exactly sure what the problem is  as your example code has several errors and doesn t really make it clear what you re trying to do  But here s how you add to a specific row of a 2D vector      declare 2D vector vector lt  vector lt int gt   gt  myVector     make new row  arbitrary example  vector lt int gt  myRow 1 5   myVector push back myRow      add element to row myVector 0  push back 1     Does this answer your question  If not  could you try to be more specific as to what you are having trouble with

User · Answer

vector lt int gt  adj n      where n is number of rows in 2d vector

User · Answer

initialize the 2D vector first   vector lt vector lt int gt  gt  matrix        initialize the 1D vector you would like to insert into matrix   vector lt int gt  row        initializing row with values   row push back val1    row push back val2         now inserting values into matrix   matrix push back row         output-     val1 val2

User · Answer

Another way to define a 2-d vector is to declare a vector of pair s     vector  lt  pair lt int int gt   gt  v     To insert values    cin  gt  gt  x  gt  gt y   v push back make pair x y       Retrieve Values    i 0 to size v   x v i  first   y v i  second    For 3-d vectors take a look at tuple and make tuple

[c++] How to implement 2D vector array?

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