I want to create array dynamically and assign value to it. e.g.
set num 0
foreach i {1 2 3} {
set count$i(sp) {$num}
incr num
set count$i(ep) [expr $num+1]
}
When I ran your sample code, this error comes up:
can't read "i(sp)": variable isn't array
which is because the $i(sp) part of count$i(sp) looks like a reference to an existing array i.
You'll want to isolate $i from (sp) with curly brackets:
set num 0
foreach i {1 2 3} {
set count${i}(sp) {$num}
incr num
set count${i}(ep) [expr $num+1]
}
which creates three arrays:
tcl8.6.8> parray count1
count1(ep) = 2
count1(sp) = $num
tcl8.6.8> parray count2
count2(ep) = 3
count2(sp) = $num
tcl8.6.8> parray count3
count3(ep) = 4
count3(sp) = $num
Note above that curly brackets around $num use the literal string $num.
You'll want to remove those curly brackets:
set num 0
foreach i {1 2 3} {
set count${i}(sp) $num
incr num
set count${i}(ep) [expr $num+1]
}
tcl8.6.8> parray count1
count1(ep) = 2
count1(sp) = 0
tcl8.6.8> parray count2
count2(ep) = 3
count2(sp) = 1
tcl8.6.8> parray count3
count3(ep) = 4
count3(sp) = 2
However, please explain exactly what you mean by "dynamically creating a Tcl array". Do you really want three separate arrays or could you have one array with more names, like this:
set num 0
foreach i {1 2 3} {
set count($i,sp) $num
incr num
set count($i,ep) [expr $num+1]
}
tcl8.6.8> parray count
count(1,ep) = 2
count(1,sp) = 0
count(2,ep) = 3
count(2,sp) = 1
count(3,ep) = 4
count(3,sp) = 2
If you can avoid using a dynamic variable name like that, do so; they're often more trouble than they're worth. (You can use “composite” element names like $i,sp instead.) Otherwise — perhaps because of other code that accesses the array — the simplest way of handling them is to use upvar to make an alias to the variable with a fixed name. In particular, upvar 0 makes an alias to a variable in the same scope:
set num 0
foreach i {1 2 3} {
upvar 0 count$i ary
set ary(sp) {$num}
incr num
set ary(ep) [expr $num+1]
}
The only problem with upvar 0 is that you can't really undo it; that's why you almost always only use it within a procedure so the aliasing goes away naturally when the procedure exits.
Variable aliases are extremely efficient within the context of a procedure, substantially more so than using compound variable names in multiple places.
Also, {$num} looks suspicious. It's not wrong code in that it has a correct interpretation, but might not do what you expect and is often indicative of a problem, as $num isn't substituted. You might prefer [list $num].
You might enjoy using a dict instead of an array:
set count {}
set num 0
foreach i {1 2 3} {
dict set count $i sp $num
incr num
dict set count $i ep [expr {$num + 1}]
}
set count ;# -> 1 {sp 0 ep 2} 2 {sp 1 ep 3} 3 {sp 2 ep 4}
dict get $count 3 ep ;# -> 4
Related
I'm trying to print out the size of my array. I've followed a few other questions like this one on Stack Overflow. However, I never get the result I want.
All I wish for in this example is for the value of 3 to be printed as I have three indexes. All I get, from both print methods is 0.
my #arr;
$arr{1} = 1;
$arr{2} = 2;
$arr{3} = 3;
my $size = #arr;
print $size; # Prints 0
print scalar #arr; # Prints 0
What am I doing wrong, and how do I get the total size of an array when declared and populated this way?
First off:
my #arr;
$arr{1} = 1;
$arr{2} = 2;
$arr{3} = 3;
is nonsense. {} is for hash keys, so you are referring to %arr not #arr. use strict; and use warnings; would have told you this, and is just one tiny fragment of why they're considered mandatory.
To count the elements in an array, merely access it in a scalar context.
print scalar #arr;
if ( $num_elements < #arr ) { do_something(); }
But you would need to change your thing to
my #arr;
$arr[1] = 1;
$arr[2] = 2;
$arr[3] = 3;
And note - the first element of your array $arr[0] would be undefined.
$VAR1 = [
undef,
1,
2,
3
];
As a result, you would get a result of 4. To get the desired 'count of elements' you would need to filter the undefined items, with something like grep:
print scalar grep {defined} #arr;
This will take #arr filter it with grep (returning 3 elements) and then take the scalar value - count of elements, in this case 3.
But normally - you wouldn't do this. It's only necessary because you're trying to insert values into specific 'slots' in your array.
What you would do more commonly, is use either a direct assignment:
my #arr = ( 1, 2, 3 );
Or:
push ( #arr, 1 );
push ( #arr, 2 );
push ( #arr, 3 );
Which inserts the values at the end of the array. You would - if explicitly iterating - go from 0..$#arr but you rarely need to do this when you can do:
foreach my $element ( #arr ) {
print $element,"\n";
}
Or you can do it with a hash:
my %arr;
$arr{1} = 1;
$arr{2} = 2;
$arr{3} = 3;
This turns your array into a set of (unordered) key-value pairs, which you can access with keys %arr and do exactly the same:
print scalar keys %arr;
if ( $elements < keys %arr ) { do_something(); }
In this latter case, your hash will be:
$VAR1 = {
'1' => 1,
'3' => 3,
'2' => 2
};
I would suggest this is bad practice - if you have ordered values, the tool for the job is the array. If you have 'key' values, a hash is probably the tool for the job still - such as a 'request ID' or similar. You can typically tell the difference by looking at how you access the data, and whether there are any gaps (including from zero).
So to answer your question as asked:
my $size = #arr;
print $size; # prints 0
print scalar #arr; # prints 0
These don't work, because you never insert any values into #arr. But you do have a hash called %arr which you created implicitly. (And again - use strict; and use warnings; would have told you this).
You are initializing a hash, not an array.
To get the "size" of your hash you can write.
my $size = keys %arr;
I just thought there should be an illustration of your code run with USUW (use strict/use warnings) and what it adds to the troubleshooting process:
use strict;
use warnings;
my #arr;
...
And when you run it:
Global symbol "%arr" requires explicit package name (did you forget to declare "my %arr"?) at - line 9.
Global symbol "%arr" requires explicit package name (did you forget to declare "my %arr"?) at - line 10.
Global symbol "%arr" requires explicit package name (did you forget to declare "my %arr"?) at - line 11.
Execution of - aborted due to compilation errors.
So USUW.
You may be thinking that you are instantiating an element of #arr when you are typing in the following code:
$arr{1} = 1;
However, you are instantiating a hash doing that. This tells me that you are not using strict or you would have an error. Instead, change to brackets, like this:
$arr[1] = 1;
I'm getting a Use of uninitialized value error. I don't know if I'm populating my multidimensional array correctly.
my #matrix;
for (my $i=1; $i<=3;$i++){
$matrix[$i][0] = 4;
}
for (my $j=1; $j<=3;$j++){
$matrix[0][$j] = 4;
}
print $matrix[0][0];
I don't understand why this doesn't work. The way I wrote it, the matrix is supposed to populate like so:
1 0
2 0
3 0
0 1
0 2
0 3
You're populating $matrix[1][0] and $matrix[0][1], but you don't store anything in $matrix[0][0].
Perl arrays start at 0 - try
my $i = 0
I want to initialize a group of array elements the same value using a single line. I know I could use a for loop, but I want to know if there is a way simpler way to do it.
for e.g., I have an array of zeros. And I want to initialize elements 4 to 9 as 1. I would think of doing something like,
my #array = (0) x 10;
for my $i (3 .. 8) {
$array[$i] = 1;
}
Why not use an array slice?
#array = (0) x 10;
#array[3..8] = (1) x 6; # or something > 6
This is easier to understand than a splice and clearer than a map.
Instead of supplying a single index, we use a list [3..8]. We have to adjust the sigil to #, because we want a list context.
One approach:
my #array = (0) x 3, (1) x 6, 0;
Another approach:
my #array = map { $_ >= 3 && $_ <= 8 ? 1 : 0 } (0 .. 9);
Or, if you mean that you've already set #array to (0) x 10, and are just looking for a one-liner to set a range of values to 1:
splice #array, 3, 6, (1) x 6;
where is the difference in TCL TK with list and array ?
I created a list of 3 arrays.
like this one in a loop
set x($idx) 1
incr idx
and later i want to return the "ret" object
list set ret { $x $x2 $x3 }
and parse them again with
lassign $data x x2 x3
but this wont work... :(
could someone please help me again.. damn tcl tk... :D:D
correct me if im not right, its not possible to build a 2dim list or array ?
Your array is called x - you can refer to its elements by set x(1) , set x(2) etc. $x2 and $x3 have no meanings in this case.
If you want a 2 dimensional array, you can simulate it in TCL as follows:
set a(1,1) 0 ;# set element 1,1 to 0
set a(1,2) 5 ;# set element 1,2 to 5
It might be easier if you just use a list of lists
set l1 [list a b c]
set l2 [list d e f]
set lol [list $l1 $l2]
You can use array get/set to pass arrays as procedure arguments / return values. For example:
proc someProc {arr} {
array set x $arr
set x(5) 0
return [array get x]
}
Example of usage:
% set a(0) -1
% set a(1) 1
% parray a
a(0) = -1
a(1) = 1
% array set b [someProc [array get a]]
% parray b
b(0) = -1
b(1) = 1
b(5) = 0
I just found myself in a position where I have two arrays in Tcl.
I'm given $W_Array and $P_Array.
I need to traverse through one array not knowing what the size of each one is before hand, and execute a command only when there is a value for both arrays. Yes the array lengths could be different.
What is the best way of doing this?
The other answers jumped to using lists, I presume you mean Tcl's array, which are also called hash maps or associative arrays.
I think you're asking for something like:
array set a1 {a 1 b 2 c 3 d 4 e 5}
array set a2 {z 0 x 1 b 2 e 99}
foreach n [array names a1] {
if {[info exists a2($n)]} {
puts "Do something with $a1($n) and $a2($n)"
}
}
# FOREACH LOOP RESULTS IN THESE TWO PRINTOUTS
Do something with 5 and 99
Do something with 2 and 2
Not sure exactly what you mean by "a value for both arrays", but tcl's foreach supports iteration over multiple arrays at once... so you can say e.g.
foreach w $W_Array p $P_Array {
if {$w == $val && $p == $val} {
...
}
}
When the arrays are not of the same length, foreach will return all values from the longest array and the empty value {} for the missing elements in any shorter arrays.
Use llength command to find out if the arrays contain a value.
if {[llength $W_Array] > 0 && [llength $P_Array] > 0} {
# Do something
}