I have input with floats stored like 1000,50, ie. the decimal points are replaced by commas.
Is there an option in K to load these numbers directly into floats ?
When using
data:("SFF" ;";",";") 0:. filename
I get 0ns, of course, because the numbers are not recognized as floats.
I load them as strings now, and convert them using ssr like
c:.:' .q.ssr'[data;",";"."]
but that is extremely slow.
Is there an option somewhere to have K load these numbers in CCC,CC format as floats directly ? Normal format and ccc,cc format are not mixed, any file has just one of them.
If there is not, I imagine that it must by quite easy to replace a "." somewhere in the Q-binary where the load-function sits, with a ",", to get a version which loads these numbers. Has anybody tried that ? Or any other tip to load big files with these numbers in reasonable time ?
Cheers,
Co
If ssr' is slow for your task you may find this tiny function useful:
c2p:{c:-1_sums count each x;p:ss[r:raze x;","];r[p]:".";(0,c) _ r}
Update: an alternative version:
c2p:{p:ss[r:raze x;","];r[p]:".";(0,-1_sums count'[x])_r}
It concatenates all strings into a single long string, finds positions of commas, replaces commas with periods then splits that long string:
q)N:1000000
q)s:string[N?100000],'",",'string N?1000
q)\t r1:ssr'[s;",";"."]
4284
q)\t r2:c2p s
242
q)r1~r2
1b
I was thinking something like find (?) combined with indexing/applying
q)N:1000000
q)s:string[N?100000],'",",'string N?1000
q)\ts {s[x;y]:"."}./:flip(til count s;s?\:",")
967 52972144
q)s
"93912.794"
"57144.788"
"77809.659"
"7839.47"
"6363.523"
"44761.244"
"65699.712"
It's not perfect but that's the general idea. I'm sure there is an easier way...
Before I get flamed, I want to say I do understand floating point numbers and things of the sort, but that doesn't seem to be my issue.
To simplify things, I'm trying to determine if a number has more than 2 decimal places. I'm doing this by multiplying the number by 100 (stored under variable "test1") and then truncating it with int() ($test2) and comparing it with an if.
$test1 = $number * 100;
$test2 = int($test1);
unless ($test1 == $test2) {
die ("test1:$test1, test2:$test2");
}
The initial $number comes from a whole series of other functions and should realistically be only two decimals, hence I'm trying to catch those that aren't (as a few entries seem to have very many decimals).
However, I just got:
test1:15, test2:14
from my die().
Can someone explain how that would happen? How can int(15) be 14?
From perldoc:
machine representations of floating-point numbers can sometimes produce counterintuitive results. For example, int(-6.725/0.025) produces -268 rather than the correct -269; that's because it's really more like -268.99999999999994315658 instead
So, the machine representation of "15" is probably something like 14.9999999999999999 and, therefore, int truncates it to 14.
Note that perldoc suggests using the POSIX functions floor or ceil instead.
In a simple, one off, case adding 0.5 to your value before int-ing it will give you what you want.
e.g.
int(14.99 + 0.5)
15
it becomes 15.49 and is int-ed "down" to 15, whereas:
int( 14.45 + 0.5 )
still gets int'ed "down" to 14.0. This is a handy trick but doesn't self document as nicely as using floor and ceil.
As a side note, the Goldberg paper on floating point arithmetic always reminds me how useful it sometimes is to have brains that are not as mindlessly precise as a computer :-)
If I wanted to check if a number had more than two decimal places, I wouldn't do math on it.
my $more_than_two = $number =~ /\d+\.\d{2}\d+\z/;
Before I do that, I might use Scalar::Util's looks_like_a_number. This method will still fail with floating point squishiness if you were expecting 14.99999 to be 15.0.
However, you should tell us what you are trying to do instead of how you are trying to do that. It's easier to give better answers.
For your questions about int, I think it's documentation tell you what you need to know. The rest is answered in the first couple of questions in perlfaq4.
I am quite new with fortran and have a question. I need to read 2 integers from the following line:
K=234, L=241, I=0
I am not interested in the last value. Just need the integers 234 and 241. I tried it with
read(20,'(3X,I3,3X,I3)')a,b
It compiles, but when I run the program I always get the error message:
At line 27 of file test.f90 (unit = 20, file = 'int_p2.dat')
Fortran runtime error: Bad value during integer read
Don't know what I am doing wrong. Can someone give me some advice?
You have strings in your line, so your READ statement ought to account for it. You should replace it with
READ(20, '(3(a2,i3,2x))') dumChar, k, dumChar, l, dumInt, dumChar
where dumChar is a character of length 2 and dumInt is an integer.
I don't see a problem in your code. (off course, your format is wrong, but should not give runtime error). Also, you are escaping chars (K,L) rather then reading them. compiler should not complain. but 3X will eat up 1 integer for K=234
Program se
Implicit None
integer :: K,L,I,a,b
open(20, file="se.in",status='old')
read(20,'(3X,I3,3X,I3)')a,b
close(20)
write(*,*)a,b
End Program se
$ cat se.in
K=234, L=241, I=0
$gfortran se.f90
$ ./a.out
34 241
If you still getting the problem, and if this are one single line you are trying to read, do
remove any space before K= in the file.
I think this is the error, as the code is reading non-integer.
So, I happened to notice that last.fm is hiring in my area, and since I've known a few people who worked there, I though of applying.
But I thought I'd better take a look at the current staff first.
Everyone on that page has a cute/clever/dumb strapline, like "Is life not a thousand times too short for us to bore ourselves?". In fact, it was quite amusing, until I got to this:
perl -e'print+pack+q,c*,,map$.+=$_,74,43,-2,1,-84, 65,13,1,5,-12,-3, 13,-82,44,21, 18,1,-70,56, 7,-77,72,-7,2, 8,-6,13,-70,-34'
Which I couldn't resist pasting into my terminal (kind of a stupid thing to do, maybe), but it printed:
Just another Last.fm hacker,
I thought it would be relatively easy to figure out how that Perl one-liner works. But I couldn't really make sense of the documentation, and I don't know Perl, so I wasn't even sure I was reading the relevant documentation.
So I tried modifying the numbers, which got me nowhere. So I decided it was genuinely interesting and worth figuring out.
So, 'how does it work' being a bit vague, my question is mainly,
What are those numbers? Why are there negative numbers and positive numbers, and does the negativity or positivity matter?
What does the combination of operators +=$_ do?
What's pack+q,c*,, doing?
This is a variant on “Just another Perl hacker”, a Perl meme. As JAPHs go, this one is relatively tame.
The first thing you need to do is figure out how to parse the perl program. It lacks parentheses around function calls and uses the + and quote-like operators in interesting ways. The original program is this:
print+pack+q,c*,,map$.+=$_,74,43,-2,1,-84, 65,13,1,5,-12,-3, 13,-82,44,21, 18,1,-70,56, 7,-77,72,-7,2, 8,-6,13,-70,-34
pack is a function, whereas print and map are list operators. Either way, a function or non-nullary operator name immediately followed by a plus sign can't be using + as a binary operator, so both + signs at the beginning are unary operators. This oddity is described in the manual.
If we add parentheses, use the block syntax for map, and add a bit of whitespace, we get:
print(+pack(+q,c*,,
map{$.+=$_} (74,43,-2,1,-84, 65,13,1,5,-12,-3, 13,-82,44,21,
18,1,-70,56, 7,-77,72,-7,2, 8,-6,13,-70,-34)))
The next tricky bit is that q here is the q quote-like operator. It's more commonly written with single quotes:
print(+pack(+'c*',
map{$.+=$_} (74,43,-2,1,-84, 65,13,1,5,-12,-3, 13,-82,44,21,
18,1,-70,56, 7,-77,72,-7,2, 8,-6,13,-70,-34)))
Remember that the unary plus is a no-op (apart from forcing a scalar context), so things should now be looking more familiar. This is a call to the pack function, with a format of c*, meaning “any number of characters, specified by their number in the current character set”. An alternate way to write this is
print(join("", map {chr($.+=$_)} (74, …, -34)))
The map function applies the supplied block to the elements of the argument list in order. For each element, $_ is set to the element value, and the result of the map call is the list of values returned by executing the block on the successive elements. A longer way to write this program would be
#list_accumulator = ();
for $n in (74, …, -34) {
$. += $n;
push #list_accumulator, chr($.)
}
print(join("", #list_accumulator))
The $. variable contains a running total of the numbers. The numbers are chosen so that the running total is the ASCII codes of the characters the author wants to print: 74=J, 74+43=117=u, 74+43-2=115=s, etc. They are negative or positive depending on whether each character is before or after the previous one in ASCII order.
For your next task, explain this JAPH (produced by EyesDrop).
''=~('(?{'.('-)#.)#_*([]#!#/)(#)#-#),#(##+#)'
^'][)#]`}`]()`#.#]#%[`}%[#`#!##%[').',"})')
Don't use any of this in production code.
The basic idea behind this is quite simple. You have an array containing the ASCII values of the characters. To make things a little bit more complicated you don't use absolute values, but relative ones except for the first one. So the idea is to add the specific value to the previous one, for example:
74 -> J
74 + 43 -> u
74 + 42 + (-2 ) -> s
Even though $. is a special variable in Perl it does not mean anything special in this case. It is just used to save the previous value and add the current element:
map($.+=$_, ARRAY)
Basically it means add the current list element ($_) to the variable $.. This will return a new array with the correct ASCII values for the new sentence.
The q function in Perl is used for single quoted, literal strings. E.g. you can use something like
q/Literal $1 String/
q!Another literal String!
q,Third literal string,
This means that pack+q,c*,, is basically pack 'c*', ARRAY. The c* modifier in pack interprets the value as characters. For example, it will use the value and interpret it as a character.
It basically boils down to this:
#!/usr/bin/perl
use strict;
use warnings;
my $prev_value = 0;
my #relative = (74,43,-2,1,-84, 65,13,1,5,-12,-3, 13,-82,44,21, 18,1,-70,56, 7,-77,72,-7,2, 8,-6,13,-70,-34);
my #absolute = map($prev_value += $_, #relative);
print pack("c*", #absolute);