Accessing table entries with iterators
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- Subject: Accessing table entries with iterators
- From: "Henderson, Michael D" <michael.d.henderson@...>
- Date: 2006年1月16日 13:59:52 -0700
The PIL says, "With proper iterators, we can traverse almost anything,
and do it in a readable fashion." I guess that I'm just not
understanding iterators.
If I have an entry like the following
entry = { timestamp = "2006年01月16日 132155"
, { "cpu" , 42.3 }
, { "fan" , 5823 }
, { "aaa" , "bbb" }
};
How would I iterate through the table to print out something like the
following?
timestamp is '2006/01/16 132155'
resource #1
type is 'cpu'
value is (number) 42.3
resource #2
type is 'fan'
value is (integer) 5823
resource #3
type is 'aaa'
value is (string) 'bbb'
If I use pairs(entry), I don't get the resources in the order that they
were created.
1
2
3
timestamp
I can get pretty close by using the iterator from PIL 7.1:
function list_iter (t)
local i = 0
local n = table.getn(t)
return function ()
i = i + 1
if i <= n then return t[i] end
end
end
if entry.timestamp then
print(entry.timestamp)
end
for k in list_iter(entry) do
print(k)
for kk in pairs(k) do
print("\t" .. kk)
print("\t\t" .. k[kk])
end
end
2006年01月16日 132155
table: 42f10
1
cpu
2
42.3
table: 47f20
1
fan
2
5823
table: 47f70
1
aaa
2
bbb
That's nice, but I want an iterator that throws an error if the
timestamp is missing or the values are missing. And I want to return the
two entries as two entries, not as a table. Would I do that by adding a
check prior to the return t[i] to verify that table.getn(t[i]) is 2? If
so, can I then just return t[i][1], t[i][2]? I guess that if I did that,
it would look like.
function tbl_iter (t)
if not t.timestamp then
error("missing timestamp")
end;
local i = 0
local n = table.getn(t)
return function ()
i = i + 1
if i <= n then
if table.getn(t[i]) == 2 then
return t[i][1] , t[i][2]
else
error("missing entries")
end
end
end
end
if entry.timestamp then
print(entry.timestamp)
end
for k1, k2 in tbl_iter(entry) do
print("type is " .. k1 .. " value is " .. k2 )
done
2006年01月16日 132155
type cpu value 42.3
type fan value 5823
type aaa value bbb
That seems to solve my problem. Man, this list is great!
Which leads me to another question. Is there a better way to write this?
This will run only a couple of hundred times a day and always against a
small table (maybe 30 entries), so performance isn't an issue, but I'd
like to make sure that I'm really understanding the right way to do
iterators.
Thanks,
Mike Henderson