Awesome that worked!<br><br>Thank you for the thorough explanation, I really appreciate it. Essentially, if I understand your example correctly, "CDEF:time=var,POP,TIME" translates to<br>"Set $time equal to that array, grab the top element from the array, grab the time from that element using TIME". It then does that for each index in the array.<br>
<br>I hope I interpreted that correctly :) <br><br>Again, thank you for quick response and explanation Alex. I hope in time I will soon be able to provide guidance to those as fresh as I am to using rrdtool!<br><br><div class="gmail_quote">
On Sat, May 8, 2010 at 10:04 AM, Alex van den Bogaerdt <span dir="ltr"><<a href="mailto:alex@vandenbogaerdt.nl">alex@vandenbogaerdt.nl</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div class="im">----- Original Message -----<br>
From: "itsmemattchung" <<a href="mailto:itsmemattchung@gmail.com">itsmemattchung@gmail.com</a>><br>
To: <<a href="mailto:rrd-users@lists.oetiker.ch">rrd-users@lists.oetiker.ch</a>><br>
Sent: Saturday, May 08, 2010 6:35 PM<br>
Subject: [rrd-users] CDEF:a=TIME throws error<br>
<br>
<br>
<br>
> I have followed the documentation<br>
> <a href="http://oss.oetiker.ch/rrdtool/tut/cdeftutorial.en.html" target="_blank">http://oss.oetiker.ch/rrdtool/tut/cdeftutorial.en.html</a><br>
> in order to calculate the derivative by using<br>
> CDEF:a=TIME<br>
> CDEF:b=PREV(a)<br>
<br>
</div>Which is, unfortunately, incorrect.<br>
<br>
My name is still on the tutorial, but the data filtering was not written by<br>
me. Nevertheless, sorry for the confusion.<br>
<br>
I have no idea who made that contribution, hopefully Tobi can tell and ask<br>
him/her for a fix.<br>
<div class="im"><br>
> "rrdtool.error: rpn expressions without DEF or CDEF variables are not<br>
> supported "<br>
> After searching around on google and through existing tickets, I ran<br>
> across<br>
> <a href="http://oss.oetiker.ch/rrdtool-trac/ticket/182" target="_blank">http://oss.oetiker.ch/rrdtool-trac/ticket/182</a> which states exactly what I<br>
> am<br>
> experiencing.<br>
><br>
> Unfortunately, I am having a hard time interpreting what oetiker posted<br>
<br>
</div>Think of DEF and CDEF as working on arrays. Each array member is an interval<br>
of time combined with a rate valid during that interval. The array members<br>
are better known as "steps", or "intervals", or CDPs (Consolidated Data<br>
Points).<br>
<br>
What TIME does, is to take the timestamp of such an interval. You can then<br>
do whatever it is you need to do. But, in order for RRDtool to find the<br>
timestamp of such an interval, it first needs the array of intervals. In<br>
"CDEF:time=TIME" there is no data thus no array thus no interval thus no<br>
timestamp.<br>
<br>
Quick fix is to put DEF "var" on the stack and remove it again:<br>
CDEF:time=var,POP,TIME<br>
I haven't verified that this will make the example work, but try it.<br>
<div class="im"><br>
> When would the syntax from the tutorial (CDEF:a=TIME) be appropriate? If<br>
> possible, can someone please elaborate on why that doesn't work, or point<br>
> be<br>
> in the right direction so I can better understand?<br>
<br>
</div>I hope this helped.<br>
cheers,<br>
<font color="#888888">Alex<br>
</font><div><div></div><div class="h5"><br>
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</div></div></blockquote></div><br>