q) ({2*x};{3*x})
How can I apply the list of functions to an input, e.g. 4, something like:
({2*x};{3*x})[4]
8 12
You should be able to use apply (#) each left (\:)
({2*x};{3*x})#\:4
Alternative approach to apply each left
q)({2*x};{3*x})[;4]
8 12
Just to generalise Michaels answer, if your function takes more than one input/parameter then you'd need to use dot-apply (.) rather than #. Dot-apply would work in both cases using:
q)({2*x};{3*x}).\:(),4
8 12
q)({y+2*x};{y+3*x}).\:(),4 100
108 112
Related
I'm trying to write a function using kdb+ which will look at the list, and find the values that simply meet two conditions.
Let's call the list DR (for data range). And I want a function that will combine these two conditions
"DR where (DR mod 7) in 2"
and
"DR where (DR.dd) in 1"
I'm able to apply them one at a time but I really need to combine them into one function. I was hoping I could do this
"DR was (DR.dd mod 7) in 2 and DR where (DR.dd) in 1"
but this obviously didn't work. Any advice?
You can utilize the and function to help with this, which is the same as &:
q)dr:.z.d+til 100
q)and
&
q)2=dr mod 7
10000001000000100000010000001000000100000010000001000000100000010000001000000..
q)1=dr.dd
00000000000000000000000001000000000000000000000000000000100000000000000000000..
q)(1=dr.dd)&2=dr mod 7
00000000000000000000000000000000000000000000000000000000100000000000000000000..
q)dr where(1=dr.dd)&2=dr mod 7
2021.02.01 2021.03.01
Its necessary wrap the first part in brackets due to how kdb reads code from right to left. This format changes slightly when doing this in a where clause, the brackets arent needed due to how each where clause is parsed, that is each clause between the commas are parsed seperately. However it is essentially doing the same thing as the code above.
q)t:([]date:dr)
q)select from t where 1=date.dd,2=date mod 7
date
----------
2021.02.01
2021.03.01
You could also do this using min to achieve similar results, like so:
DR where min(1=DR.dd;2=DR mod 7)
What is (!). called in kdb?
and are below use cases valid to use (!). to convert a list to a dictionary or are there better ways and other uses of (!). ?
Example:
q)(!). (`A`B;(`C`D`E;`F`G`H));
q).[(!);flip (`A`B;`C`D;`E`F)]
I cannot find any documentation on the use cases on (!). in kdb tutorials. Please share any information on (!). and its uses?
It's a version of apply & yep your use case is valid. The reason the operator is wrapped in parentheses is because it itself is a dyadic infix operator as is dot apply (.)
If you attempt to apply it as is, your expression is like so, which Q doesn't like
// infixOp infixOp operand
q)+ . 4 5
'
[0] + . 4 5
^
Wrapping the operator within parentheses effectively transforms it so the expression now becomes
// operand infixOp operand
q)(+). 4 5
9
If you define a function which can't be used infix, then there's no need to wrap it
q)f:+
q)4 f 5
'type
[0] 4 f 5
^
q)f . 4 5
9
If using apply with bracket notation as in your example, there's no need to wrap the function
q).[+;4 5]
9
https://code.kx.com/q/ref/apply/#apply-index
https://code.kx.com/q/basics/syntax/#parentheses-around-a-function-with-infix-syntax
Jason
In terms of use-cases, I find it very useful when defining dictionaries/tables as configs particularly when dictionaries are too wide (horizontal) for the screen or when it's more useful to see fields/mappings vertically as pairs. From a code/script point of view that is.
For example:
mapping:(!) . flip(
(`one; 1);
(`two; 2);
(`three; 3));
is much easier to read when scanning through a q script than
mapping2:`one`two`three!1 2 3
when the latter gets very wide.
It makes no difference to the actual dictionary of course because as Jason pointed out it's the same thing.
I've copy the exact example in q for mortals as follows:
q)h:hopen `:D:/q4m/raw
q)h[42]
548i
q)h 10 20 30
548i
q)hclose h
q)get `:D:/q4m/raw
'D:/q4m/raw
[0] get `:D:/q4m/raw
Look into the directory, the file was created there. Why can't I get it?
Instead, if I do:
q)h:hopen `:D:/q4m/L
q)h[42]
628i
q)h[10 20 30]
628i
q)hclose h
q)get `:D:/q4m/L
0 1 2 3 4 42 10 20 30
Things get normal, why?
After testing the given code I believe your issue may be in how you intialise the file.
I assume in the code that works that you use some variation of
`:D:/q4m/L set til 5
before.
However this is not done for
`:D:/q4m/raw
If you were to use
`:D:/q4m/raw set til 5
or alternatively
.[`:D:/q4m/raw;();:;()]
beforehand then the first set of code will work.
Additionally, if we look at the binary using
read1 `:D:/q4m/raw
and
read1 `:D:/q4m/L
and the output does not include 07 near the beginning then it is not being recognised as a proper kdb list. That is, hopen simply appends to the binary file instead of amending it. (If you notice the 05 byte that indicates length of the list, this doesn't increase when you add via the handle).
eg.
The first method you get
q)read1 `:D:/q4m/raw
0x2a000000000000000a0000000000000014000000000000001e00000000000000
which dosen't really mean anything in q.
The second method gives
q)read1 `:D:/q4m/L
0xfe2007000000000005000000000000000000000000000000010000000000000002000000000..
which is a proper kdb list (notice the 07 which indicates type).
If you wish to instead just read in /q4m/raw then I suggest setting an empty list, hopen to that list and pass it `:D:/q4m/raw as follows
q)`:empty set 0#0
`:empty
q)h:hopen `:empty
q)h read1 `:D:/q4m/raw
3i
q)get `:empty
42 10 20 30
This will only work if all entries are the same type.
I'm endeavoring to create a system to generalize rules from input text. I'm using reVerb to create my initial set of rules. Using the following command[*], for instance:
$ echo "Bananas are an excellent source of potassium." | ./reverb -q | tr '\t' '\n' | cat -n
To generate output of the form:
1 stdin
2 1
3 Bananas
4 are an excellent source of
5 potassium
6 0
7 1
8 1
9 6
10 6
11 7
12 0.9999999997341693
13 Bananas are an excellent source of potassium .
14 NNS VBP DT JJ NN IN NN .
15 B-NP B-VP B-NP I-NP I-NP I-NP I-NP O
16 bananas
17 be source of
18 potassium
I'm currently piping the output to a file, which includes the preceding white space and numbers as depicted above.
What I'm really after is just the simple rule at the end, i.e. lines 16, 17 & 18. I've been trying to create a script to extract just that component and put it to a new file in the form of a Prolog clause, i.e. be source of(banans, potassium).
Is that feasible? Can Prolog rules contain white space like that?
I think I'm locked into getting all that output from reVerb so, what would be the best way to extract the desirable component? With a Perl script? Or maybe sed?
*Later I plan to replace this with a larger input file as opposed to just single sentences.
This seems wasteful. Why not leave the tabs as they are, and use:
$ echo "Bananas are an excellent source of potassium." \
| ./reverb -q | cut --fields=16,17,18
And yes, you can have rules like this in Prolog. See the answer by #mat. You need to know a bit of Prolog before you move on, I guess.
It is easier, however, to just make the string a a valid name for a predicate:
be_source_of with underscores instead of spaces
or 'be source of' with spaces, and enclosed in single quotes.
You can use probably awk to do what you want with the three fields. See for example the printf command in awk. Or, you can parse it again from Prolog directly. Both are beyond the scope of your current question, I feel.
sed -n 'N;N
:cycle
$!{N
D
b cycle
}
s/\(.*\)\n\(.*\)\n\(.*\)/\2 (\1,\3)/p' YourFile
if number are in output and not jsut for the reference, change last sed action by
s/\^ *[0-9]\{1,\} \{1,\}\(.*\)\n *[0-9]\{1,\} \{1,\}\(.*\)\n *[0-9]\{1,\} \{1,\}\(.*\)/\2 (\1,\3)/p
assuming the last 3 lines are the source of your "rules"
Regarding the Prolog part of the question:
Yes, Prolog facts can contain whitespace like this, with suitable operator declarations present.
For example:
:- op(700, fx, be).
:- op(650, fx, source).
:- op(600, fx, of).
Example query and its result, to let you see the shape of terms that are created with this syntax:
?- write_canonical(be source of(a, b)).
be(source(of(a,b))).
Therefore, with these operator declarations, a fact like:
be source of(a, b).
is exactly the same as stating:
be(source(of(a,b)).
Depending on use cases and other definitions, it may even be an advantage to create this kind of facts (i.e., facts of the form be/1 instead of source_of/2). If this is the only kind of facts you need, you can simply write:
source_of(a, b).
This creates no redundant wrappers and is easier to use.
Or, as Boris suggested, you can use single quotes as in 'be source of'/2.
In order to debug a very complex set of functions, I want to isolate a subfunction from the workspace in order to make different test. Therefore a need selected values from the function workspace to be defined already. By setting a break point at the specific position I can "look" into the current workspace by displaying the values in the console, like the variable HF33
HF33 =
1.0777 0.0865 0.0955
-0.1891 0.8110 -0.1889
0.0935 0.0846 1.0755
Is there some function / script that could convert this result to a new Matlab expression that can be pasted somewhere else (for example at the head of a new script), e.g.:
HF33 = [ 1.0777, 0.0865, 0.0955;
-0.1891, 0.8110, -0.1889;
0.0935, 0.0846, 1.0755 ];
With that I could test the subfunction and its behavior by easily changing the given values and see whats happening without having the huge debug workspace running.
Is there some easy function like res2exp(HF33)?
First: Create this function to get the variable name
function out = varname(var)
out = inputname(1);
end
you can print it direct to console:
fprintf('%s =%s\n',varname(varToSave),mat2str(varToSave));
Or use fopen and fprint to write it in a file
fop = fopen('filename','w');
fprint(fop,'%s = %s' ,varname(varToSave),mat2str(varToSave));
fclose(fop);
I think this will help you
It might be a function like mat2str() you are looking for but it will not give exactly the printout you are asking for. Here is an example of how it could be used:
>> A = magic(4)
A =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
>> B = mat2str(A)
B =
[16 2 3 13;5 11 10 8;9 7 6 12;4 14 15 1]
And if you want the output to be totally copy/paste-able you could use:
disp(['C = ',mat2str(A)])
C = [16 2 3 13;5 11 10 8;9 7 6 12;4 14 15 1]
I made this up just now. It is not formatted beautifully, but it achieves what you are trying to do - if I understand you correctly.
a = [ 2 3 4 5
4 5 5 6
3 4 5 6];
fprintf('\nb = [\n\n');
disp(a);
fprintf(']\n\n');
Copy and paste this and see if it does what you want. It's also very simple code, so you could modify it if the spacing and newline characters aren't where you want them.
You could also make a small function out of this if you wanted to.
If you want me to make a function of it, let me know... I can do it tomorrow. But you can probably figure it out.
Ehh, I just made the function. It didn't take long.
function reprint_matrix(matrix)
var_name = inputname(1);
fprintf('\n%s = [\n\n', var_name);
disp(matrix);
fprintf(']\n\n');
end
I'm not sure what you are looking for, but I think this will help you:
http://www.mathworks.com/matlabcentral/fileexchange/24447-generate-m-file-code-for-any-matlab-variable/content/examples/html/gencode_example.html
Did not use it because I use mat-files to transfer data.
You can combine it with the clipboard function:
clipboard('copy',gencode(ans))
Though there are several ways to write variables to text, saving variables as text is definitely bad practice if it can be avoided. Hence, the best advice I can give you is to solve your problem in a different way.
Suppose you want to use HF33 in your subfunction, then here is what I would recommend:
First of all, save your variable of interest:
save HF33 HF33
Then when you are in the function where you want to use this variable:
load HF33
This assumes that your working directory (not workspace) is the same in both cases, but otherwise you can simply add the path in your save or load command. If you want to display it you can now simply call the variable HF33 without a semicolon (this is probably the only safe way to display it exactly the way you expect in all cases).
Note that this method can easily be adapted to transfer multiple variables at once.