remove rows in a matrix

[martindunne]

hi there i have a grid of numbers 8x16
i would like to remove rows y 1,3,5,7,9,11,13,15
is there an equation i can use for this or do i need to specify onlt the numbers i need in another array.

thanks

[Thomas1965]

Arrays have fixed size so you can't delete rows or cols.
You could create a new array with the desired amout of rows and cols, copy the values over.
A better option would be to use vectors.

[martindunne]

thank you
my code defines a start point(0) and an end point (120) but i want to remove 8- 15, 24-31, 40-47,56-63,72-79,88-95 and 104 to 111

is this at all possible.

thanks already

[lastchance]

#include<iostream>
#include<vector>
using namespace std;

using matrix = vector< vector<double> >;         // Just an alias to save typing

//--------------------------------------

void print( const matrix &M )                    // Output a matrix
{
   for ( auto &row : M )
   {
      for ( auto e : row ) cout << e << '\t';
      cout << '\n';
   }
}

//--------------------------------------

matrix evenRows( const matrix &M )               // Copy even rows into a new matrix
{
   matrix result;
   for ( int i = 0; i < M.size(); i += 2 ) result.push_back( M[i] );
   return result;
}

//--------------------------------------

int main()
{
   int ROWS = 16, COLS = 8;
   matrix M( ROWS, vector<double>( COLS ) );     // Create a ROWS x COLS matrix
   for ( int i = 0; i < ROWS; i++ )
   {
      for ( int j = 0; j < COLS; j++ ) M[i][j] = COLS * i + j;
   }

   cout << "Original matrix:\n";    print( M );

   matrix E = evenRows( M );

   cout << "\nEven rows only:\n";   print( E );
}

Original matrix:
0	1	2	3	4	5	6	7	
8	9	10	11	12	13	14	15	
16	17	18	19	20	21	22	23	
24	25	26	27	28	29	30	31	
32	33	34	35	36	37	38	39	
40	41	42	43	44	45	46	47	
48	49	50	51	52	53	54	55	
56	57	58	59	60	61	62	63	
64	65	66	67	68	69	70	71	
72	73	74	75	76	77	78	79	
80	81	82	83	84	85	86	87	
88	89	90	91	92	93	94	95	
96	97	98	99	100	101	102	103	
104	105	106	107	108	109	110	111	
112	113	114	115	116	117	118	119	
120	121	122	123	124	125	126	127	

Even rows only:
0	1	2	3	4	5	6	7	
16	17	18	19	20	21	22	23	
32	33	34	35	36	37	38	39	
48	49	50	51	52	53	54	55	
64	65	66	67	68	69	70	71	
80	81	82	83	84	85	86	87	
96	97	98	99	100	101	102	103	
112	113	114	115	116	117	118	119

[martindunne]

this seem very usefull but not sure if it is what i need here is some code:

#define GRID_X 16
#define GRID_Y 8
#define LAUNCHPAD_GRID_X 8
#define LAUNCHPAD_GRID_Y 8

#define GRID_STATE(b,x,y) *(b + x + (y * GRID_X) )


#define LP_MIDI_NOTE_ON     0x90
#define LP_MIDI_NOTE_OFF    0x80
#define LP_MIDI_POLY_AT     0xA0
#define LP_MIDI_CC          0xB0
#define LP_MIDI_PGM         0xC0
#define LP_MIDI_CHAN_PR     0xD0
#define LP_MIDI_PB          0xE0
#define LP_MIDI_OTHER       0xF0


// midi note/cc numbers
#define LP_NOTE_PAD_START       00											
#define LP_NOTE_PAD_END         (LP_NOTE_PAD_START + 120)
//static uint8_t LP_NOTE_PAD[64] =      {   0,  1,  2,  3,  4,  5,  6,  7,
                                         //16, 17, 18, 19, 20, 21, 22, 23,
										 //32, 33, 34, 35, 36, 37, 38, 39, 
										 //48, 49, 50, 51, 52, 53, 54, 55,
										 //64, 65, 66, 67, 68, 69, 70, 71,
										 //80, 81, 82, 83, 84, 85, 86, 87,
										 //96, 97, 98, 99, 100,101,102,103,
										 //112,113,114,115,116,117,118,119
                                       //};


#define LP_ENCODER_CC_TEMPO     14
#define LP_ENCODER_CC_SWING     15

void launchpad_handle_midi(void* self, union event_data* evin) {
    struct dev_launchpad *launchpad = (struct dev_launchpad *) self;

    uint8_t type = evin->midi_event.data[0] & 0xF0;

    // uint8_t ch = ev->midi_event.data[0] & 0x0F;
    // determine if midi message is going to be interpretted or just sent on
    switch (type) {
    case LP_MIDI_NOTE_ON:
    case LP_MIDI_NOTE_OFF: {
        int8_t note = evin->midi_event.data[1];
        int8_t data = evin->midi_event.data[2];
        if (note >= LP_NOTE_PAD_START && note <= LP_NOTE_PAD_END) {
            if (launchpad->pad_mode_ == LPPM_GRID) {
                // send grid key event
                int x = ((note - LP_NOTE_PAD_START)% LAUNCHPAD_GRID_X  ) + (launchpad->grid_page_ * LAUNCHPAD_GRID_X);
                int y = LAUNCHPAD_GRID_Y - ((note - LP_NOTE_PAD_START) / LAUNCHPAD_GRID_X) - 1;
                union event_data *ev = event_data_new(EVENT_GRID_KEY);
                ev->grid_key.id = launchpad->dev_.id + LAUNCHPAD_DEV_OFFSET;
                ev->grid_key.x = x;
                ev->grid_key.y = y;
                ev->grid_key.state = (type == LP_MIDI_NOTE_ON) && (data > 0);
                // fprintf(stderr, "key %d\t%d\t%d\t%d\n", ev->grid_key.id, ev->grid_key.x, ev->grid_key.y , ev->grid_key.state);
                event_post(ev);
            } else { // LPPM_NOTE
                const int tonic = 0;
                const int rowOffset = 5;
                int x = (note - LP_NOTE_PAD_START) % LAUNCHPAD_GRID_X;
                int y =  (note - LP_NOTE_PAD_START) / LAUNCHPAD_GRID_X;
                int noteout = (launchpad->midi_octave_ * 12)  + (y * rowOffset) + x + tonic;
                evin->midi_event.data[1] = noteout;
                // fprintf(stderr, "midi  0x%02x\t%d\t%d\n", evin->midi_event.data[0], evin->midi_event.data[1], evin->midi_event.data[2]);
                event_post(evin);

                uint8_t clr = PAD_NOTE_ON_CLR;
                if (type == LP_MIDI_NOTE_OFF || data == 0) {
                    const int scale = 0b101011010101;
                    int note_s = (y * rowOffset) + x;
                    int i = note_s %  12;
                    int v = (scale & (1 << ( 11 - i)));
                    clr = (i == 0 ? PAD_NOTE_ROOT_CLR : (v > 0 ? PAD_NOTE_IN_KEY_CLR : PAD_NOTE_OFF_CLR));
                }
                dev_launchpad_midi_send_note(self, note, clr);
          
            }
        }
        break;

commented out my array as if i use a table i cannot use the if command on line 48