I cannot change the value of global variable a within f because it has the same name as a local variable: when function returns, a is still 1 instead of 12.
a: 1
f: func[a][set 'a a]
>> f 12
== 12
>> a
== 1
How can I refer to global variable a ? Isn't set supposed to only refer to global variable ? Am I obliged to change my local variable name to do so or is there a way to keep both name ?
Use system/words/ path prefix to force read or write access to a word in global context:
>> a: 1
>> f: func[a][system/words/a: a]
== func [a][system/words/a: a]
>> f 12
== 12
>> a
== 12
Related
I am confused with a tcsh shell script issue. (for work, no choice in shell, I'm stuck with it)
The enableThingN items below are shell enviroment variables set by other things before running this csh script, using tcsh shell. These are not set within the same script here at all, only evaluated here.
Error message is:
enableThing1: Undefined variable.
Code is:
if ( ( $?enableThing1 && ($enableThing1 == 1) ) || \
( $?enableThing2 && ($enableThing2 == 1) ) || \
( $?enableThing3 && ($enableThing3 == 1) ) || \
( $?enableThing4 && ($enableThing4 == 1) ) ) then
set someScriptVar = FALSE
else
set someScriptVar = TRUE
endif
So, as I understand things, the first part of the big if condition is to check if enableThing1 is defined at all or not, using the $?enableThing1 magic. If it is defined, then move on and check the value is 1 or something else. If not defined, then skip the ==1 part of the check for the same shell variable, and move on to see if enableThing2 is defined at all or not, and so on.
As it seems like I am checking for existence, and intend to avoid checking value if it is not defined at all, where have I gone wrong?
I have searched here on stackoverflow and on Google at large, but there are few results and don't get me to an answer, such as:
https://stackoverflow.com/questions/16975968/what-does-var-mean-in-csh
An if statement to check the value of the variable requires that the variable exists.
if ( ( $?enableThing1 && ($enableThing1 == 1) ) || \
# ^ this will fail if the variable is not defined.
So the if condition turns into
if ( ( 0 && don'tknowaboutthis ) || \
and it falls flat.
Assuming you don't want an if ladder, and functionality to add to this list of variables to check for, you can try the following solution:
#!/bin/csh -f
set enableThings = ( enableThing1 enableThing2 enableThing3 enableThing4 ... )
# setting to false initially
set someScriptVar = FALSE
foreach enableThing ($enableThings)
# since we can't use $'s in $? we'll have to do something like this.
set testEnableThing = `env | grep $enableThing`
# this part is for checking if it exists or not, and if it's enabled or not
if (($testEnableThing != "") && (`echo $testEnableThing | cut -d= -f2` == 1 )) then
# ^ this is to check if the variable is defined ^ this is to take the part after the =
# d stands for delimiter
# for example, the output of testEnableThing, if it exists, would be enableThing1=1
# then we take that and cut it to get the value of the variable, in our example it's 1
# if it exists and is enabled, set your someScriptVar
set someScriptVar = TRUE
# you can put a break here since it's irrelevant to check
# for other variables after this becomes true
break
endif
end
This works because we are only working with one variable, "testEnableThing", which is always defined due to the way this works. It can be a blank string, but it will be defined so our if statement won't fall flat.
Hope this solves it for you.
Let me start by saying that I understand that what I'm asking about in the title is dubious practice (as explained here), but my lack of understanding concerns the syntax involved.
When I first tried to bind a scalar to a sigilless symbol, I did this:
my \a = $(3);
thinking that $(...) would package the Int 3 in a Scalar (as seemingly suggested in the documentation), which would then be bound to symbol a. This doesn't seem to work though: the Scalar is nowhere to be found (a.VAR.WHAT returns (Int), not (Scalar)).
In the above-referenced post, raiph mentions that the desired binding can be performed using a different syntax:
my \a = $ = 3;
which works. Given the result, I suspect that the statement can be phrased equivalently, though less concisely, as: my \a = (my $ = 3), which I could then understand.
That leaves the question: why does the attempt with $(...) not work, and what does it do instead?
What $(…) does is turn a value into an item.
(A value in a scalar variable ($a) also gets marked as being an item)
say flat (1,2, (3,4) );
# (1 2 3 4)
say flat (1,2, $((3,4)) );
# (1 2 (3 4))
say flat (1,2, item((3,4)) );
# (1 2 (3 4))
Basically it is there to prevent a value from flattening. The reason for its existence is that Perl 6 does not flatten lists as much as most other languages, and sometimes you need a little more control over flattening.
The following only sort-of does what you want it to do
my \a = $ = 3;
A bare $ is an anonymous state variable.
my \a = (state $) = 3;
The problem shows up when you run that same bit of code more than once.
sub foo ( $init ) {
my \a = $ = $init; # my \a = (state $) = $init;
(^10).map: {
sleep 0.1;
++a
}
}
.say for await (start foo(0)), (start foo(42));
# (43 44 45 46 47 48 49 50 51 52)
# (53 54 55 56 57 58 59 60 61 62)
# If foo(42) beat out foo(0) instead it would result in:
# (1 2 3 4 5 6 7 8 9 10)
# (11 12 13 14 15 16 17 18 19 20)
Note that variable is shared between calls.
The first Promise halts at the sleep call, and then the second sets the state variable before the first runs ++a.
If you use my $ instead, it now works properly.
sub foo ( $init ) {
my \a = my $ = $init;
(^10).map: {
sleep 0.1;
++a
}
}
.say for await (start foo(0)), (start foo(42));
# (1 2 3 4 5 6 7 8 9 10)
# (43 44 45 46 47 48 49 50 51 52)
The thing is that sigiless “variables” aren't really variables (they don't vary), they are more akin to lexically scoped (non)constants.
constant \foo = (1..10).pick; # only pick one value and never change it
say foo;
for ^5 {
my \foo = (1..10).pick; # pick a new one each time through
say foo;
}
Basically the whole point of them is to be as close as possible to referring to the value you assign to it. (Static Single Assignment)
# these work basically the same
-> \a {…}
-> \a is raw {…}
-> $a is raw {…}
# as do these
my \a = $i;
my \a := $i;
my $a := $i;
Note that above I wrote the following:
my \a = (state $) = 3;
Normally in the declaration of a state var, the assignment only happens the first time the code gets run. Bare $ doesn't have a declaration as such, so I had to prevent that behaviour by putting the declaration in parens.
# bare $
for (5 ... 1) {
my \a = $ = $_; # set each time through the loop
say a *= 2; # 15 12 9 6 3
}
# state in parens
for (5 ... 1) {
my \a = (state $) = $_; # set each time through the loop
say a *= 2; # 15 12 9 6 3
}
# normal state declaration
for (5 ... 1) {
my \a = state $ = $_; # set it only on the first time through the loop
say a *= 2; # 15 45 135 405 1215
}
Sigilless variables are not actually variables, they are more of an alias, that is, they are not containers but bind to the values they get on the right hand side.
my \a = $(3);
say a.WHAT; # OUTPUT: «(Int)»
say a.VAR.WHAT; # OUTPUT: «(Int)»
Here, by doing $(3) you are actually putting in scalar context what is already in scalar context:
my \a = 3; say a.WHAT; say a.VAR.WHAT; # OUTPUT: «(Int)(Int)»
However, the second form in your question does something different. You're binding to an anonymous variable, which is a container:
my \a = $ = 3;
say a.WHAT; # OUTPUT: «(Int)»
say a.VAR.WHAT;# OUTPUT: «(Scalar)»
In the first case, a was an alias for 3 (or $(3), which is the same); in the second, a is an alias for $, which is a container, whose value is 3. This last case is equivalent to:
my $anon = 3; say $anon.WHAT; say $anon.VAR.WHAT; # OUTPUT: «(Int)(Scalar)»
(If you have some suggestion on how to improve the documentation, I'd be happy to follow up on it)
Let's say I have
block: [a 1 b 2 c 3]
I want
[1 2 3]
Something like this is clunky and it doesn't work because I use word type (I'd like to have it word with word not string):
block: [a 1 b 2 c 3]
block2: []
counter: -1
foreach 'element block [
counter: negate counter
if counter append block2 element
]
The EXTRACT function should fit the bill here:
>> extract/index [a 1 b 2 c 3] 2 2
== [1 2 3]
It's fairly versatile for this type of thing.
>> help extract
USAGE:
EXTRACT series width
DESCRIPTION:
Extracts a value from a series at regular intervals.
EXTRACT is a function! value.
ARGUMENTS:
series [series!]
width [integer!] "Size of each entry (the skip)".
REFINEMENTS:
/index => Extract from an offset position.
pos [integer!] "The position".
/into => Provide an output series instead of creating a new one.
output [series!] "Output series".
I am trying to create a record from list using Record.make:
declare
L=[z [a b] [1 2]]
{Record.make L.1 L.2 0}
but getting an error:
Expected type: feature
At argument: 1
How to make a second argument L.2 to be A 'feature' type? I assume L.2 is a [a b] list.
Record.make creates a record with fresh (i.e. unbound) values. For example:
R = {Record.make label [a b]}
Maybe you want List.toRecord instead:
R = {List.toRecord label [a#1 b#2]}
Is there a way to plot a function based on values from a text file?
I know how to define a function in gnuplot and then plot it but that is not what I need.
I have a table with constants for functions that are updated regularly. When this update happens I want to be able to run a script that draws a figure with this new curve. Since there are quite few figures to draw I want to automate the procedure.
Here is an example table with constants:
location a b c
1 1 3 4
2
There are two ways I see to solve the problem but I do not know if and how they can be implemented.
I can then use awk to produce the string: f(x)=1(x)**2+3(x)+4, write it to a file and somehow make gnuplot read this new file and plot on a certain x range.
or use awk inside gnuplot something like f(x) = awk /1/ {print "f(x)="$2 etc., or use awk directly in the plot command.
I any case, I'm stuck and have not found a solution to this problem online, do you have any suggestions?
Another possibilty to have a somewhat generic version for this, you can do the following:
Assume, the parameters are stored in a file parameters.dat with the first line containing the variable names and all others the parameter sets, like
location a b c
1 1 3 4
The script file looks like this:
file = 'parameters.dat'
par_names = system('head -1 '.file)
par_cnt = words(par_names)
# which parameter set to choose
par_line_num = 2
# select the respective string
par_line = system(sprintf('head -%d ', par_line_num).file.' | tail -1')
par_string = ''
do for [i=1:par_cnt] {
eval(word(par_names, i).' = '.word(par_line, i))
}
f(x) = a*x**2 + b*x + c
plot f(x) title sprintf('location = %d', location)
This question (gnuplot store one number from data file into variable) had some hints for me in the first answer.
In my case I have a file which contains parameters for a parabola. I have saved the parameters in gnuplot variables. Then I plot the function containing the parameter variables for each timestep.
#!/usr/bin/gnuplot
datafile = "parabola.txt"
set terminal pngcairo size 1000,500
set xrange [-100:100]
set yrange [-100:100]
titletext(timepar, apar, cpar) = sprintf("In timestep %d we have parameter a = %f, parameter c = %f", timepar, apar, cpar)
do for [step=1:400] {
set output sprintf("parabola%04d.png", step)
# read parameters from file, where the first line is the header, thus the +1
a=system("awk '{ if (NR == " . step . "+1) printf \"%f\", $1}' " . datafile)
c=system("awk '{ if (NR == " . step . "+1) printf \"%f\", $2}' " . datafile)
# convert parameters to numeric format
a=a+0.
c=c+0.
set title titletext(step, a, c)
plot c+a*x**2
}
This gives a series of png files called parabola0001.png,
parabola0002.png,
parabola0003.png,
…, each showing a parabola with the parameters read from the file called parabola.txt. The title contains the parameters of the given time step.
For understanding the gnuplot system() function you have to know that:
stuff inside double quotes is not parsed by gnuplot
the dot is for concatenating strings in gnuplot
the double quotes for the awk printf command have to be escaped, to hide them from gnuplot parser
To test this gnuplot script, save it into a file with an arbitrary name, e.g. parabolaplot.gplot and make it executable (chmad a+x parabolaplot.gplot). The parabola.txt file can be created with
awk 'BEGIN {for (i=1; i<=1000; i++) printf "%f\t%f\n", i/200, i/100}' > parabola.txt
awk '/1/ {print "plot "$2"*x**2+"$3"*x+"$4}' | gnuplot -persist
Will select the line and plot it
This was/is another question about how to extract specific values into variables with gnuplot (maybe it would be worth to create a Wiki entry about this topic).
There is no need for using awk, you can do this simply with gnuplot only (hence platform-independent), even with gnuplot 4.6.0 (March 2012).
You can do a stats (check help stats) and assign the values to variables.
Data: SO15007620_Parameters.txt
location a b c
1 1 3 4
2 -1 2 3
3 2 1 -1
Script: (works with gnuplot 4.6.0, March 2012)
### read parameters from separate file into variables
reset
FILE = "SO15007620_Parameters.txt"
myLine = 1 # line index 0-based
stats FILE u (a=$2, b=$3, c=$4) every ::myLine::myLine nooutput
f(x) = a*x**2 + b*x + c
plot f(x) w l lc rgb "red" ti sprintf("f(x) = %gx^2 + %gx + %g", a,b,c)
### end of script
Result: