maybe this question seems stupid... I would like to fprintf a dataset formatted in rows and columns. I know the procedure so far
for(i=0;i<number_of_rows;i++)
{
for(j=0;j<number_of_columns;j++)
fprintf(file,"%g\t",array[i][j]);
fprintf(file,"\n");
}
What essentially does this code is to fill up first the rows and then the columns. I have datasets that are created by columns. Thus, I want to fill up every column before I pass to the next one. I don't know before the runtime the length of the output data in order to make a proper 2D array. And I need to print out first a whole column, then the other. How can I do this?
And I need to print out first a whole column, then the other. How can I do this?
That would involve appending to a previously printed line. And, as you may know, adding content into a file involves rewriting the entire rest of the file. You can probably guess that would be incredibly inefficient and also complicated to implement.
I don't know before the runtime the length of the output data in order to make a proper 2D array
If your problem is the length of the data, then I assume that by proper 2D array you mean that you intend to pad each cell of a column to be the same width.
In that case, I recommend not to waste time on the idea of writing column first. Instead, calculate the widths at runtime. First sprintf into a matrix of strings and calculate the length of each cell. Then print the matrix of strings using the calculated lengths.
Related
A truncated version of my data is in the form shown in the screenshot below: three columns of 5 unique names. The names appear in any order and in any position but never repeat in a single row.
My goal is to create an array that contains the number of times Adam appears in each row. I can fill down the formula=countif(A2:C2,$I$2) in a new column, or if I write the array manually for each row, it looks like:
={countif(A2:C2,$I$2);countif(A3:C3,$I$2);countif(A4:C4,$I$2);countif(A5:C5,$I$2);countif(A6:C6,$I$2)}
Where cell I2 contains "Adam". Of course, this is not feasible for large data sets.
I know that arrays are effectively cells turned into ranges, but my main issue is that the cell I'm trying to transform already references a range, and I don't know how to tell the software to apply the countif down each row (i.e. I intuitively would like to do something like countif((A2:C2):(A99:C99),"Adam") but understand that's not how spreadsheets work).
My goal is ultimately to perform some operations on the corresponding array but I think I'm comfortable enough with that once I can get the array formula I'm looking for.
try:
=ARRAYFORMULA(IF(A2:A="",,MMULT(IF(A2:C="Adam", 1, 0), {1;1;1})))
I want to add a constant to the second column of an array.
I do this as shown below:
Where for illustration the values are as follows:
What is the most efficient way of adding a constant to an array column?
With a question about efficiency you should supply number. For anything lower than a 1000 x 1000 2D array I can't measure the difference. Usually it is best to simply test it.
Here the code for testing (same answer as crossrulz)
With a 10000 x 10000 array option 2 becomes about 10 times faster.
One comment unless you are in a very high demanding situation, readability is usually preferred over efficiency. In my opinion option 2 is more readable since it has no for loop and the constant is presented as a constant instead of an array.
But you can get more efficient than that by using the In Place Element structure. The image below shows two different ways to add 5 to a column. The second one avoids making a memory copy of the entire array. Indexing out a column of an array with Index Array and then modifying it requires a shift of underlying memory format, even though the array is going to be put back in the Replace Array Subset. The In Place Element structure gives enough context to LabVIEW for it to recognize that the Add can be done without data copies.
Index Array to get the second column, add your constant, and then Replace Array Subset to replace the second column.
I've got a bigger table with one column that I want to focus on, containing designation and a number. I want to simply sum the numbers that meet the criteria based on a designation.
For the simplification, I made an exercising sheet (on the pic) where I split second column into two - one string and one numeric. Since my file is quite large with many columns that would need this it would be inconvenient.
In the left column it's easy to solve the problem, it could be even easier with simple SUMIF function, but an array SUM(IF... function is, at least I think, only viable option here.
So I solved the first table with array function, but what confuses me is how to modulate the TRUE statement. Simple replacement of C:C
with
VALUE(MID(F:F;4;4))
which would format my cells to get the numbers from string does not work that way - returns zero in E12 field. F12 is just application of string to number for last cell, F10.
THIS formula does not work, even adapting to different versions of the tool.
I could use VB but if possible anyhow I would like to avoid it since parts will be shared on mobile phones.
Any ideas? Thanks a lot!
Left table was split, right original format
The array formula which you used can be replaced by the SumIf formula like below...
=SUMIF(B:B,"B",C:C)
Also without the helper column, you can use the Sumproduct formula to achieve the desired output.
But don't refer the whole column in the formula like in the above SumIf formula.
Try this..
=SUMPRODUCT((B1:B10="B")*MID(F1:F10,FIND(",",F1:F10)+1,255)*1)
Change the ranges as per your requirement but remember to make them equal in size.
I'm at a loss for what to do in my program (written in C). There is a large matrix of numbers (an image) that I am processing. The processing happens one line at a time, with reference to the previous line, so I only need to access two lines of numbers at a time.
Originally, I tried a 2 by X array but once I save the information for the third line, the array is upside down with the third line of the image in the first row of the array and the second line of the image in the second row of the image.
Is there a better way to correct this other than simply copying the second row of the array to the first row? Maybe it wouldn't be so bad, but I would imagine doing that for every other line of the image would be expensive. Should I use two pointers on the image instead?
I apologize if this is a common thing that can be easily looked up but I couldn't figure out how to begin looking. If anyone needs clarification, let me know. Thank you very much!
Diagram of what numbers I need access to:
http://www.gliffy.com/go/publish/5968966
I suppose that you are processing the image as you read it, or as you decompress it, or some such, for if you already had the whole thing in memory in usable form then you would just use that.
I see two reasonably good alternatives:
Instead of hard-coding the indices of the earlier and later lines in your 2 by x array, use variables to track which row contains which line.
Use a 1-D array for each line, and use pointers to track which one contains the current line and which one contains the previous line.
(Though really, those boil down to pretty much the same thing.) Either way, you can avoid needless copying.
Let's assume you have:
struct rbg_t bitmap[X][Y];
To get a window of dimensions X by 2, it is like this:
struct rgb_t *first_line = bitmap[0], *second_line=bitmap[1];
Then you can process the two lines like so:
for(int i=0;i<X;++i)
{
do_work(first_line[i], second_line[i]);
}
To shift the window down by one, you can do this:
first_line+=sizeof(struct rgb_t)*X;
second_line+=sizeof(struct rgb_t)*X;
Where X is the width of the bitmap
I want to be able to store a series of strings of different sizes such as
userinput=['AJ48 NOT'; 'AH43 MANA'; 'AS33 NEWEF'];
This of course returns an error as the number of columns differs per row. I'm aware that all that is needed for this to work is adequate spaces in the first and second rows. However I need to be able to put this into an array without forcing the user to add these spaces on his/her own. Is there a command that allows me to do this? If possible I'd also like to know why this problem doesn't arise with numbers e.g.
a=[1; 243; 23524];
You cannot do this with standard Matlab arrays. A string is really just a vector of characters in Matlab. And you cannot have a matrix with rows of different lengths.
You can, however, use a cell array:
userinput={'AJ48 NOT'; 'AH43 MANA'; 'AS33 NEWEF'};
disp(userinput{1});
Be aware that there are many situations where cell arrays don't work like normal arrays.
To just answer to your last part of your question; simply because strings may be variable length but numbers (in Matlab) are fixed length. It's one of the main ideas of arrays to let them hold only fixed sizes entities (for example because the need of efficient look up), see more on the topic here.