Firebase limit_to_last(1) doesn't work as expected - python-3.x

I have data in firebase that is recording temperature like the following:
I will eventually have a number of weeks, the key starts at 1, next week the key will be 2 then 3 etc etc
I wanted to write a query that gives me the data from the last week (The week with the highest numbered key)
I have this line of code in a python script:
rtn = root.child('bedroom').child('weeks').order_by_key().limit_to_last(1).get()
print(rtn)
This is what is printed out:
[None, {'date_time': '2018-06-08 19:38:41.634010', 'temperature': '21'}]
Why is None at the start of the array? Do I assume it is always here? I want to use the data in the second location of the array. But if it isn't always in the second location of the array my code will then break. I thought that query would return an array of size 1.
I think when I was testing I did see the array only being 1 element in size with the json structure as the first element but I cannot confirm this.

When you use numeric keys (like you do), Firebase may interpret your data as an array. To learn more about this, read Best Practices: Arrays in Firebase.
If this array coercion is a problem for your app, I recommend prefixing the number with a fixed string, e.g. "week_1" or even better "week_01 (since that may you can filter on ranges of weeks).

Related

Excel formula to sum an array of items from a lookup list

I'm trying to make my monthly transaction spreadsheet less work-intensive but I'm running up against problems outputting my category lookups as an array. Right now I have a table with all my monthly transactions and I want to create another table with monthly running totals. What I've been doing is manually summing each entry from each category, but I'd love to automate the process. Here's what I have:
=SUM(INDEX(Transactions[Out], N(IF(1,MATCH(I12,Transactions[Category],FALSE)))))
I've also tried using AGGREGATE in place of SUM but it still only returns the first value in the category. The N(IF()) was supposed to force INDEX to return all the matches as an array, but it's not working. I found that trick online, with no explanation of why it works, so I really don't know how to fix it. Any ideas?
Just in case anyone ever looks at this thread in the future, I was able to find a simpler solution to my problem once I implemented the Transactions[Category]=I12 method. SUM, itself will take an array as an argument, so all I had to do was form an array of the values I wanted to keep from Transactions[Out] range. I did this by adjusting the method Ron described above, but instead of using 1/(Transactions[Category]=I12 I used 1/IF(Transactions[Category]=I12, 1,1000) and surrounded that by a FLOOR(*resulting array*, .01) which rounded all the thousandth's down to zero and didn't yield any #DIV/0! errors.
Then! I realized that the simplest way to get the actual numbers I wanted, rather than messing with INDEX or AGGREGATE, was to multiply the range Transactions[Out] by the binary array from the IF test. Since the range is a table, I know they will always be the same size. And SUM automatically multiplies element by element and then adds for operations like this.
(The result is a "CSE" formula, which I guess isn't everyone's favorite. I'm still not 100% clear on what it means: just that it outputs data in a single cell, rather than over multiple cells. But in this context, SUM should only output a single number, so I'm not sure why I need CSE... A problem for another day!)
In your IF, the value_if_true clause needs to return an array of the desired row numbers from the array.
MATCH does not return an array of values; it only returns a single value which, with the FALSE parameter, will be the first value. That's why INDEX is only returning the first value.
One way to return an array of values:
Transactions[Category]=I12
will return an array of {TRUE,FALSE,FALSE,TRUE,...} depending on if it matches.
You can then multiply that by the Row number to get the relevant row on the worksheet.
Since you are using a table, to obtain the row number in the data body array, you have to subtract the row number of the Header row.
But now we are going to have an array which includes 0's for the non-matching entries, which is not good for us as a row number argument for the INDEX function.
So we get rid of that by using the AGGREGATE function with the ignore errors argument set after we do change the equality test to 1/(Transactions[Category]=I12) which will create DIV/0 errors for the non-matchers.
Putting it all together
=SUM(INDEX(Transactions[Out],AGGREGATE(15,6,1/(Transactions[Category]=I12)*ROW(Transactions)-ROW(Transactions[#Headers]),ROW(INDIRECT("1:"&COUNTIF(Transactions[Category],$I$12))))))
You may need to enter this with CSE depending on your version of Excel.
Also, if you have a lot of these formulas, you may want to change the k argument for AGGREGATE to use the INDEX function (non-volatile) instead of the volatile INDIRECT function.
=SUM(INDEX(Transactions[Out],AGGREGATE(15,6,1/(Transactions[Category]=I12)*ROW(Transactions)-ROW(Transactions[#Headers]),ROW(INDEX($A:$A,1,1):INDEX($A:$A,COUNTIF(Transactions[Category],$I$12),1)))))
Edit
If you have Excel/O365 with dynamic arrays and the FILTER function, you can greatly simplify the above to the normally entered:
=SUM(FILTER(Transactions[Out],Transactions[Category]=I12))

Comparing two arrays - Horizontal vs Vertical

What is the case
I'm trying to compare two arrays. For simplicity sake let's assume we want to know how often the values of one array exist in the other array.
My referenced/lookup array data sits in A1:A3
Apple
Lemon
Pear
My search array is NOT in the worksheet, but written {"Apple","Pear"}
Problem
So to know how often our search values exists in the lookuparray we can apply a formula like:
{=SUMPRODUCT(--(range1=range2))}
However, {=SUMPRODUCT(--({"Apple","Pear"}=A1:A3))} produces an error. In other words the lookup array wasn't working as expected.
What did work was using TRANSPOSE() function to create a horizontal array from my data first using {=SUMPRODUCT(--({"Apple","Pear"}=TRANSPOSE(A1:A3)))} resulting in the correct answer of 2!
It seems as though my typed array is automatically handled as an horizontal array, and my data obviously was originally vertical.
To test my hypotheses I tried another formula:
{=SUMPRODUCT(--({"Apple","Pear"}={"Apple","Lemon","Pear"}))}
Both are typed arrays, so with above logic it would both be horizontal arrays, perfectly able to work without using TRANSPOSE(), however this returns an error! #N/A
Again {=SUMPRODUCT(--({"Apple","Pear"}=TRANSPOSE({"Apple","Lemon","Pear"})))} gave a correct answer of 2.
Question
Can someone please explain to me:
The reasoning why horizontal can't be compared to vertical arrays.
Why a typed array would automatically be handled as horizontal
Why in my test of the hypotheses the second typed array was handled as vertical.
I'm really curious, and would also be happy to be linked to appropriate documentation as so far I have not been able to find any.
This might be an easy one to answer, though I can't seem to get my head around the logic.
Can someone please explain to me:
The reasoning why horizontal can't be compared to vertical arrays.
This is actually possible, and you can also compare horizontal arrays with other horizontal arrays.
The reason you have been getting the error is because of the mismatch in the length of the array. Consider the following arrays:
Doing =SUMPRODUCT(--(B3:D3=F3:G3)) is the same (on excel's english version, I'm not 100% sure on the delimiters on other versions) as =SUMPRODUCT(--({"Apple","Lemon","Pear"}={"Apple","Pear"})) and results in =SUMPRODUCT(--(Apple=Apple, Lemon=Pear, Pear=???)), that is the nth element of the first array is compared to the nth element of the second array, and if there is nothing to match --the 3rd element in the 1st array is Pear but there is no 3rd element for the 2nd array-- then you get N/A.
When you compare two arrays, one vertical and one horizontal, excel actually 'expands' the final array. Consider the following (1row x 3col and 2row x 1col):
Doing =SUMPRODUCT(--(B3:D3=F3:F4)) is the same as =SUMPRODUCT(--({"Apple","Lemon","Pear"}={"Apple";"Pear"})) and results in =SUMPRODUCT(--(Apple=Apple, Lemon=Apple, Pear=Apple; Apple=Pear, Lemon=Pear, Pear=Pear)). Basically it feels like Excel expanded the two arrays like this (3col x 2row):
This 'expansion' only happens when one array is 1 row high and the other is 1 column wide I believe, so if you take arrays that have something different, then excel will go back to trying to compare an element with 'nothing' to give N/A (you can use the Evaluate Formula feature under Formula tab to help):
So essentially excel is getting something a bit similar to this, where the first array is multiplied to the second array, giving the result array:
But since the last row and last column involve blanks, you get N/A there.
Why a typed array would automatically be handled as horizontal
In your question, it would seem that , delimit rows, so with =SUMPRODUCT(--({"Apple","Pear"}=A1:A3)) you are observing similar to the comparison of two rows in my first example, while with =SUMPRODUCT(--({"Apple","Pear"}=TRANSPOSE(A1:A3))), you are getting the 'expansion' occurring.
As stated in the comments, on the English version of excel, , delimits columns and ; delimits rows, as can be observed in this simple example where I supply an array with 2 rows and 3 columns, excel shows {0,0,0;0,0,0}:
Why in my test of the hypotheses the second typed array was handled as vertical.
TRANSPOSE simply switches an array from vertical to horizontal (and vice versa), but depending on what you are trying to do, you'll get different results as per the first part of my answer, so you'll either have N/A when excel cannot match an item of an array with another item of the other array, or 'expansion' of the two arrays that results in a bigger array.

Assigning and reading multidimensional arrays in Python

I'm stumped.
for a in range(0,500): #500 is a highly variable number but using it for example purposes
b = findall(r'<(.*?)>', d) # d will return a highly number variable number of matches could be anywhere from 45-10000
c.append([b])
print(c[0][1])
This returns the error because everything from 'b' goes into c[0][0]. I can understand this. The question is how do I split 'b' apart so I can put it into c so I can
print(c[0][234])
and get it give me back the 235, err element 234 of the 1, err 0, line?
This is a situation like I said above where the number of times going through 'b' will be variable, at least for right now until I get the entire file prepped I can only that 'b' in the end will be way north of 10,000 and probably closer to 100,000 by the time I have all the data collection finished. The number of elements that are stored can and will be highly variable depending on the file that they come from. They are all coming from a csv file but I'm hoping to not to deal with adding in any 'complexity' by going out and having to deal with the csv module...since I've never used it before and that will probably just lead to more questions.
I have tried something similiar to...different variables naturally so things would be appropriately matched up
d = list(zip(*(e.split(',') for e in b)))
all this has did is split on each and every letter versus on the comma.
Your error is coming from the square brackets you have in c.append([b]). The brackets create an extra list that contains the list b. So rather than a two dimensional data structure, you're ending up with three dimensions. Your indexing fails because c[0][1] is trying to get a second value from the middle list (which only ever has one item in it).
You might get what you want with c[0][0][1] instead. But you probably don't actually want that extra level in your data structure. You can avoid creating it by using: c.append(b)

Frequency() with arrays: adds an element to return arrays

I'm using the following formula as named formula (via name manager). It is then used in a larger sumproduct(). The goal is to ensure that with an array calculation, the calculation is only made once for certain groups of rows (e.g. you have the same data repeated accross many rows for category A. I only need to know how many people are in category A once).
=IF(FREQUENCY(IF(LEN(tdata[reportUUID])>0,MATCH(tdata[reportUUID],
tdata[reportUUID],0),0),IF(LEN(tdata[reportUUID])>0,MATCH(tdata[reportUUID],
tdata[reportUUID],0),0))>0,TRUE)
Let's step through the results one by one with the evaluate formula in Excel. Sorry for the screenshot, but Excel doesn't allow to copy actual steps with real data....
In order of steps:
In the last image, there's now a 7th item in my array. I only have 6 row of data, hence why for the previous steps I only had 6 items in the array, as was expect.
This is messing up my calculations, because the return array from this function gets multiplied by others arrays which all have 6 items (or whatever is the number of data rows I have).
What is this 7th item, and how can I either get ride of it or prevent it from return errors?
I did try to wrap some formula into iferror() or ifna(), however it doesn't feel clean. I feel this might backfire and isn't a strong way to handle this. I rather take it at the source....
EDIT: For example of use with other arrays:
{=SUMPRODUCT(--IFERROR(((tdata[_isVisible]=1)*(f_uniqueUUIDfactor),0))}
Where f_uniqueUUIDfactor is the formula from the initial post. tdata[_isVisible]=1 is used as a way to filter data on the dashboard (e.g. through dropdown, the users can set ranges for dates, and with VBA I hide the rows in the raw data NOT within the range).
The point is that sumproduct() ends up multipliying each raw data row thogheter as 0 & 1 s, so that only those meeting all the criterias get returned. The IFERROR() above is the workaround for the extra array element introduced by frequency(). It works as is, but if a cleaner way exists I'd prefer that. I would also be keen on understanding why that elements get added.
This is a good example of why it is preferable to use multiple, recursive IF statements when evaluating arrays over multiple criteria, rather than form the product of those arrays.
Firstly, though, before coming to the reason for that statement, I should point out a few minor technical inaccuracies/flaws with your construction also.
1) By including a value_if_false clause in your constructions being passed as FREQUENCY's data_array and bins_array parameters, you are risking incorrect results, since zero is a valid numerical to be considered by FREQUENCY, whereas a Boolean FALSE (which would be the equivalent entry in the resulting array had you omitted the value_if_false clause altogether) is disregarded by this function.
2) MATCH with an exact (i.e. 0, or FALSE) match_type parameter is a relatively resource-heavy construction, particularly if the range to be considered is quite large. As such, and since it is not necessary to use this construction for FREQUENCY's bins_array parameter, it is preferable to use the more efficient:
ROW(tdata[reportUUID])-MIN(ROW(tdata[reportUUID]))+1
Moreover, note that repetition of the IF(LEN construction is also not necessary within this second parameter.
In all, then:
IF(FREQUENCY(IF(LEN(tdata[reportUUID])>0,MATCH(tdata[reportUUID],tdata[reportUUID],0)),ROW(tdata[reportUUID])-MIN(ROW(tdata[reportUUID]))+1)>0,TRUE)
is considerably more rigorous and more efficient than the version you give.
To answer your main question, it is well-documented that FREQUENCY always returns an array having a number of entries one greater than that of the bins_array passed.
As mentioned in my comment to your post, the resolution to the problem you are facing largely depends on precisely what further manipulation you are intending for the resulting array.
However, let's assume for the sake of an explanation that you simply wish to multiply the array resulting from your FREQUENCY construction by some other column within your table, tdata[Column2] say, and then sum the result.
The difference between:
=SUM(IF(FREQUENCY(IF(LEN(tdata[reportUUID])>0,MATCH(tdata[reportUUID],tdata[reportUUID],0)),ROW(tdata[reportUUID])-MIN(ROW(tdata[reportUUID]))+1)>0,TRUE)*tdata[Column2])
i.e. using multiplication of the two arrays, and:
=SUM(IF(FREQUENCY(IF(LEN(tdata[reportUUID])>0,MATCH(tdata[reportUUID],tdata[reportUUID],0)),ROW(tdata[reportUUID])-MIN(ROW(tdata[reportUUID]))+1)>0,tdata[Column2]))
i.e. using a straightforward IF clause, is here crucial.
In fact, the former will always return an error, whereas the latter, in general, will not.
The reason is that the former will resolve to (assuming that your table has e.g. 10 rows' worth of data and assuming some random Boolean results to the FREQUENCY construction):
=SUM(IF({TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE},TRUE)*tdata[Column2])
which is, since the value_if_true clause is superfluous here:
=SUM({TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE}*tdata[Column2])
whereas the second construction I give will resolve to:
=SUM(IF({TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE},tdata[Column2]))
The two may look identical, but the fact that the former is using multiplication to resolve the array, whereas the latter is not, is the key difference.
Although in both cases the array resulting from the FREQUENCY construction, i.e.:
{TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE}
comprises 11 entries (i.e. 1 more than the number of entries in the second array being considered), the difference is that, when you then attempt to multiply an 11-element array with a 10-element array (i.e. tdata[Column2]), Excel, rather than outright disallowing such an operation, artificially redimensions the smaller of the two arrays such that it matches the dimensions of the larger.
In doing so, however, any additional entries are automatically set as #N/A error values.
Effectively, then:
=SUM({TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE}*tdata[Column2])
is resolved as:
=SUM({TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE}*{38;67;49;3;10;11;97;20;3;57;#N/A})
i.e., as mentioned, the second, 10-element array is redimensioned to one of 11 elements in an attempt to form a legitimate operation. And, as also mentioned, that 11th element is #N/A, which means of course that the entire construction will also result in that value.
In the non-multiplication version, however, i.e.:
=SUM(IF({TRUE;TRUE;TRUE;FALSE;FALSE;FALSE;FALSE;FALSE;TRUE;TRUE;FALSE},tdata[Column2]))
although the same redimensiong also takes place, we are saved by our use of an IF clause in place of multiplication, since the above resolves to:
=SUM(IF({TRUE;FALSE;TRUE;FALSE;TRUE;TRUE;TRUE;FALSE;TRUE;FALSE;FALSE},{38;67;49;3;10;11;97;20;3;57;#N/A}))
and the Boolean FALSE in the 11th position here 'overrides' the error value in the equivalent position from the second array, since the above resolves to:
=SUM({38;FALSE;49;FALSE;10;11;97;FALSE;3;FALSE;FALSE})
Regards

nested excel functions with conditional logic

Just getting started in Excel and I was working with a database extract where I need to count values only if items in another column are unique.
So- below is my starting point:
=SUMPRODUCT(COUNTIF(C3:C94735,{"Sharable Content Object Reference Model 1.2","Authored SCORM/AICC content","Authored External Web Content"}))
what i'd like to figure out is the syntax to do something like this-
=sumproduct (Countif range1 criteria..., where range2 criteria="is unique value")
Am I getting this right? The syntax is a bit confusing, and I'm not sure I've chosen the right functions for the task.
I just had to solve this same problem a week ago.
This method works even when you can't always sort on the grouping column (J in your case). If you can keep the data sorted, #MikeD 's solution will scale better.
Firstly, do you know the FREQUENCY trick for counting unique numbers? FREQUENCY is designed to create histograms. It takes two arrays, 'data' and 'bins'. It sorts 'bins', then creates an output array that's one longer than 'bins'. Then it takes each value in 'data' and determines which bin it belongs in, incrementing the output array accordingly. It returns the array. Here's the important part: If a value appears in 'bins' more than once, any 'data' value meant for that bin goes in the first occurrence. The trick is to use the same array for both 'data' and 'bins'. Think it through, and you'll see that there's one non-zero value in the output for each unique number in the input. Note that it only counts numbers.
In short, I use this:
=SUM(SIGN(FREQUENCY(<array>,<array>)))
to count unique numeric values in <array>
From this, we just need to construct arrays containing numbers where appropriate and text elsewhere.
In the example below, I'm counting unique days when the color is red and the fruit is citrus:
This is my conditional array, returning 1 or true for the rows I'm interested in:
($A$2:$A$10="red")*ISNUMBER(MATCH($B$2:$B$10,{"orange","grapefruit","lemon","lime"},0))
Note that this requires ctrl-shift-enter to be used as an array formula.
Since the value I'm grouping by for uniqueness is text (as is yours), I need to convert it to numeric. I use:
MATCH($C$2:$C$10,$C$2:$C$10,0)
Note that this also requires ctrl-shift-enter
So, this is the array of numeric values within which I'm looking for uniqueness:
IF(($A$2:$A$10="red")*ISNUMBER(MATCH($B$2:$B$10,{"orange","grapefruit","lemon","lime"},0)),MATCH($C$2:$C$10,$C$2:$C$10,0),"")
Now I plug that into my uniqueness counter:
=SUM(SIGN(FREQUENCY(<array>,<array>)))
to get:
=SUM(SIGN(FREQUENCY(
IF(($A$2:$A$10="red")*ISNUMBER(MATCH($B$2:$B$10,{"orange","grapefruit","lemon","lime"},0)),MATCH($C$2:$C$10,$C$2:$C$10,0),""),
IF(($A$2:$A$10="red")*ISNUMBER(MATCH($B$2:$B$10,{"orange","grapefruit","lemon","lime"},0)),MATCH($C$2:$C$10,$C$2:$C$10,0),"")
)))
Again, this must be entered as an array formula using ctrl-shift-enter. Replacing SUM with SUMPRODUCT will not cut it.
In your example, you'd use something like:
=SUM(SIGN(FREQUENCY(
IF(ISNUMBER(MATCH($C$3:$C$94735,{"Sharable Content Object Reference Model 1.2","Authored SCORM/AICC content","Authored External Web Content"},0)),MATCH($J$3:$J$94735,$J$3:$J$94735,0),""),
IF(ISNUMBER(MATCH($C$3:$C$94735,{"Sharable Content Object Reference Model 1.2","Authored SCORM/AICC content","Authored External Web Content"},0)),MATCH($J$3:$J$94735,$J$3:$J$94735,0),"")
)))
I'll note, though, that scaling might be a problem on data sets as large as yours. I tested it on larger data sets, and it was fairly fast on the order of 10k rows, but really slow on the order of 100k rows, such as yours. The internal arrays are plenty fast, but the FREQUENCY function slows down. I'm not sure, but I'd guess it's between O(n log n) and O(n^2) depending on how the sort is implemented.
Maybe this doesn't matter - none of this is volatile, so it'll just need to calculate once upon refreshing the data. If the column data is changing, though, this could be painful.
Asuming the source data is sorted by the key value [A], start with determining the occurence of the key column
B2: =IF(A2=A1;B1+1;1)
Next determine a group sum
C2: =SUMIF($A$2:$A$9;A2;$B$2:$B$9)
A key is unique if its group sum is exactly 1
D2: =(C2=1)
To count records which match a certain criterium AND are unique, include column D in a =IF(AND(D2, [yourcondition];1;0) and sum this column
Another option is to asume a key unique within a sorted list if it is unequal to both its predecessor and successor, so you could find the unique records like
E2: =AND(A2<>A1;A2<>A3)
G2: =IF(AND(E2;F2="this");1;0)
E and G can of course be combined into one single formula (not sure though if that helps ...)
G2(2): =IF(AND(AND(A2<>A1;A2<>A3);F2="this");1;0)
resolving unnecessarily nested AND's:
G2(3): =IF(AND(A2<>A1;A2<>A3;F2="this");1;0)
all formulas in row 2 should be copied down to the end of the list

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