var example is a 2-dimension array. example.length will give values like 14.3
But how can I get an integer for the length of example in second dimension, like 3 in this case?
Thank you!
If the array is homogeneous (which is always the case when such an array is the result of a getValues() call in a spreadsheet range for example) you can simply write :
example[0].length
EDIT : a few comments to be more clear ...
The 2D array you get from example = range.getValues() is always an array of rows data.
The number of rows is represented by example.length and the inner array length (representing rows content) is always example[0].length, which is actually the number of columns
Related
If I have a two-dimensional array, how can I get the number of columns ?
I can get number of lines with Array.length(o) where o is an 5*10 matrix, which returns 5.
But how to do with columns?
Assuming there is at least one "line", and that the column arrays are of equal length, just take the length of the first "column" array:
Array.length m.(0)
If there are no lines however, this will raise an exception.
I know mapping 2D array into 1D array has been asked many times, but I did not find a solution that would fit a where the column count varies.
So I want get a 1-dimensional index from this 2-dimensional array
Col> _0____1____2__
Row 0 |_0__|_1__|_2__|
V 1 |_3__|_4__|
2 |_5__|_6__|_7__|
3 |_8__|_9__|
4 |_10_|_11_|_12_|
5 |_13_|_14_|
The normal formula index = row * columns + column does not work, since after the 2nd row the index is out of place.
What is the correct formula here?
EDIT:
The specific issue is that I have a list of items in with the layout like in the grid, but a one dimensional array for the data. So while looping through the elements in the UI, I need to get the correct data, but can only get the row and column for that element. I need to find a way to turn a row/column value into an index for the data-array
Bad picture trying to explain it
A truly optimal answer (or even a provably correct one) will depend on the language you are using and how it lays out memory for such arrays.
However, taking your question simply at face value, you have to know what the actual length of each row is in order to calculate a 1D index.
So either the row length follows some pattern that can be inferred from the data, or you have (or can write) a rlen = rowLength( 2dTable, RowNumber) function.
Then, depending on how big the tables are and how fast you need to run, you can calculate a 1D index from the 2d table by adding all the previous row lengths until the current row length is less than the 2d column index.
or build a 1d table of the row lengths (or commulative rowlengths) so you can scan it and so only call your rowlength function for each row only once.
With a better description of your problem, you might get a better answer...
For your example which alternates between 3 and 2 columns you can construct a formula:
index = (row / 2) * (3 + 2) + (row % 2 ? 3 : 0) + column
(C-like syntax, assuming integer division)
In general though, the one and only way to implement what you're doing here, jagged arrays, is to make an array of arrays, a.k.a. an Iliffe vector. That means, use the row number as index into an array of pointers which point to the individual row arrays containing the actual data.
You can have an additional 1D array having the length of the columns say "length". Then your formula is index=sum {length(i)}+column. i runs from 0 to row.
I have a query which I am trying to solve
I know that one can use strcmp(s1,s2) to compare two different strings to see whether they are the same. It gives 1 if that is the case.
However, how would one tackle this problem if you have a variable length array full of strings and you want to the whether all strings in the array are the same.
For example: ['NACA64A010' 'NACA64A010' 'NACA64A010' 'NACA64A010'] we can see that all the strings are the same in this array. However, how would one go about with using strcmp(s1,s2).
Thanks guys!
If you want all pairwise comparisons between strings: call ndgrid to generate indices of all combinations, and then index into your cell array of strings and call strcmp:
x = {'NACA64A010' 'NACA64A010' 'NACA64A010' 'NACA64A010'};
[ii, jj] = ndgrid(1:numel(x));
result = strcmp(x(ii), x(jj));
In this case
result =
1 1 1 1
1 1 1 1
1 1 1 1
1 1 1 1
because all strings are the same.
You probably had a pairwise comparison using strcmp in mind, but you can use it directly on cell arrays:
x={'NACA64A010' 'NACA64A010' 'NACA64A010' 'NACA64A010'}
result=all(strcmpi(x{1},x(2:end)))
Compare the first element to the remaining elements. It returns true only if all elements are equal. For a pairwise comparison you could us:
[~,~,c]=unique(x);
result=bsxfun(#eq,c,c.')
If you're solving the problem with a matrix (i.e. every row is a string) there are no particularly nice solutions in my opinion, but if your strings are contained into a cell array, things are getting easier and nicer.
So we start by creating such cell array:
myStrings={'NACA64A010' 'NACA64A010' 'NACA64A010' 'NACA64A010'};
where each cell contains a string. This will make your code more robust as well since every string can have a different length (this is not true if you concatenate all your strings in a matrix).
Then you specify which string you want to find inside such cell array:
stringThatMustBeTested='NACA64A010';
Now you can use cellfun(), which is a function that applies another function to every cell of a given cell array as follows:
results=cellfun(#(x) strcmp(x,stringThatMustBeTested),myStrings);
Such line simply means "apply strcmp() to every generic cell x inside myStrings and compare the cell with stringThatMustBeTested".
Variable results will be a logical output in which element j will be true if the j-th cell in your cell array is equal to the string you want to test. If results is entirely composed by 1s (which you can check as if sum(results)==length(results)), then all the strings are the same in myStrings (given that stringThatMustBeTested is the unique string in your cell array but anyways, this solution can be extended to a broader string search inside a cell).
My array contains a string in the first row
how can I sum the array from the 2nd row to the Nth/1442th row (as in my example) disregarding the negative signs present in the column?
for example, my code for an array called data2 is:
S = sum(data2(2,15):data2(1442,15));
so sum all of the elements from row 2 to row 1442 in column 15.
This doesn't work but it also does not have anything to deal with the absolute value of whatever row its checking
data is from a .csv:
You should do something like this:
sum(abs(data(2:1442,15)));
The abs function will find the absolute value of each value in the array (i.e. disregard the negative sign). data(2:1442,15) will grab rows 2-1442 of the 15th column, as you wanted.
EDIT: apparently data is a cell array, so you could do the following, I think:
sum(abs([data{2:1442,15}]));
Ok so it looks like you have a constant column so
data2(2,15) = -0.02
and further down
data2(1442,15) = -0.02 %(I would assume)
So when you form:
data2(2,15):data2(1442,15)
this is essential like trying to create an array but of a single value since:
-0.02:-0.02
ans =
-0.0200
which of course gives:
>> sum(-0.02:-0.02)
ans =
-0.0200
What you want should be more like:
sum(data2(2:1442,15))
That way, the index: 2:1442, forms a vector of all the row references for you.
To disregard the negative values:
your answer = sum(abs(data2(2:1442,15)))
EDIT: For a cell array this works:
sum(abs(cell2mat(data2(2:1442,15))))
I have data that is of the following form:
'of' 45001 23366 21859591 52876216 0 45001
'on' 40649 23226 17940625 44201973 0 40649
'my' 37976 18338 11277975 47042676 0 37976
'me' 28707 18134 6546887 36222235 0 28707
I am wondering how in MATLAB I go about sorting say column 2 from largest to smallest but keep all the other rows associated with the one that's being sorted - this is stored in a cell array also.
Any help would be appreciated.
Although you're dealing with a cell array, the answer actually ends up being the same as that listed for numeric arrays in the closely-related questions I linked to in my above comment: simply use the function SORTROWS. Here's how you can sort the rows of your cell array according to the values in the second column (in descending order):
sortedCellArray = sortrows(cellArray,-2);
NOTE: It should be noted that the documentation for SORTROWS doesn't appear to explicitly say that the function will work with cell array inputs, but it does have an example showing that it works for them just like it does for any other array.