Randomly selecting a member from a repeat group (with side conditions)

Support
1

Hi all,

I am implementing a household survey using ODK/SurveyCTO. I have a repeat
group which collects names and sexes of household members and would like to
randomly select the name of one boy from this repeat group. I have troubles
figuring out how to do it.

As explained here
https://groups.google.com/forum/#!msg/opendatakit/AkSq6VRSA_Y/Lt-RmBs33S8J,
without the condition that this person must be a boy this would be easy:
Just generate a random position of the repeat group and take the household
member at that position. But in my case, this person might be a girl and
repeating the procedure doesn't guarantee that the next time it will be a
boy.

Is there any way to do this? I have been trying to generate a new repeat
group with only the boys, but I haven't succeeded. The main problem for
this seems to be that I can not pass on information from one instance to
the next in a repeat group (from position(..) - 1 to position(..)). With
this, you could implement any "loop" to solve these kind of problems.

Thanks!
Wouter

2

Hi Wouter,

Here's a method that might work, though I'm not positive...

In your repeat, add an "isboy" field with a calculation like (modified to
test gender as appropriate to your gender field):

if(${gender}=1, 1, 0)

Also add a "boyname" field with a calculation like (modified again in the
same way):

if(${gender}=1, ${name}, '')

(Note that the second parameter to the if function is a pair of single
quotation marks.)

Now, outside the repeat you can have a "numboys" field with a calculation
like:

sum(${isboy})

And a "boynames" field with a calculation like:

join(' ', ${boyname})

(Note that the first parameter to the join function is a single space
inside single quotation marks. If you need to pull the boy's name from a
choice label, you'd call the jr:choice-name function in the above.)

So here you should have the number of boys and a list of their names. The
question is whether count-selected(${boynames}) returns the number of boys
or the total number of repeats. If the former, then you can use
random-once() and selected-at() to draw one of the boys; if the latter,
then this method won't work because the "boysnames" list still includes
entries (though blank) for the girls. If that's the case, then what we
really need is a way to collapse multiple spaces down to one (since, in the
space-separated list of names, there are multiple spaces for girls); post
back and we'll see if somebody else has an idea for how to do that. (We
might need to add a replace function of some sort... Such a need has come
up several times before.)

Best,

Chris

··· On Thu, Jan 2, 2014 at 3:21 AM, Wouter Gelade wrote:

Hi all,

I am implementing a household survey using ODK/SurveyCTO. I have a repeat
group which collects names and sexes of household members and would like to
randomly select the name of one boy from this repeat group. I have troubles
figuring out how to do it.

As explained here
https://groups.google.com/forum/#!msg/opendatakit/AkSq6VRSA_Y/Lt-RmBs33S8J,
without the condition that this person must be a boy this would be easy:
Just generate a random position of the repeat group and take the household
member at that position. But in my case, this person might be a girl and
repeating the procedure doesn't guarantee that the next time it will be a
boy.

Is there any way to do this? I have been trying to generate a new repeat
group with only the boys, but I haven't succeeded. The main problem for
this seems to be that I can not pass on information from one instance to
the next in a repeat group (from position(..) - 1 to position(..)). With
this, you could implement any "loop" to solve these kind of problems.

Thanks!
Wouter

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3

Hello Chris,

Has anyone been able to come up with a solution to this?

currently in a form am designing, am able to pull out the choice list for
men who are at a certain age to respond to a certain question but this
comes with blank spaces for the women who have also taken up instance
spaces in the repeat group count.

Desperately need a solution, to be able to concatenate for men only without
the blank spaces.

Thanks!!!

··· On Thursday, January 2, 2014 at 12:46:17 PM UTC+1, Christopher Robert wrote: > > Hi Wouter, > > Here's a method that might work, though I'm not positive... > > In your repeat, add an "isboy" field with a calculation like (modified to > test gender as appropriate to your gender field): > > if(${gender}=1, 1, 0) > > > Also add a "boyname" field with a calculation like (modified again in the > same way): > > if(${gender}=1, ${name}, '') > > > (Note that the second parameter to the if function is a pair of single > quotation marks.) > > Now, outside the repeat you can have a "numboys" field with a calculation > like: > > sum(${isboy}) > > > And a "boynames" field with a calculation like: > > join(' ', ${boyname}) > > > (Note that the first parameter to the join function is a single space > inside single quotation marks. If you need to pull the boy's name from a > choice label, you'd call the jr:choice-name function in the above.) > > So here you should have the number of boys and a list of their names. The > question is whether count-selected(${boynames}) returns the number of boys > or the total number of repeats. If the former, then you can use > random-once() and selected-at() to draw one of the boys; if the latter, > then this method won't work because the "boysnames" list still includes > entries (though blank) for the girls. If that's the case, then what we > really need is a way to collapse multiple spaces down to one (since, in the > space-separated list of names, there are multiple spaces for girls); post > back and we'll see if somebody else has an idea for how to do that. (We > might need to add a replace function of some sort... Such a need has come > up several times before.) > > Best, > > Chris > > > > On Thu, Jan 2, 2014 at 3:21 AM, Wouter Gelade <wouter...@gmail.com > wrote: > >> Hi all, >> >> I am implementing a household survey using ODK/SurveyCTO. I have a repeat >> group which collects names and sexes of household members and would like to >> randomly select the name of one boy from this repeat group. I have troubles >> figuring out how to do it. >> >> As explained here >> https://groups.google.com/forum/#!msg/opendatakit/AkSq6VRSA_Y/Lt-RmBs33S8J, >> without the condition that this person must be a boy this would be easy: >> Just generate a random position of the repeat group and take the household >> member at that position. But in my case, this person might be a girl and >> repeating the procedure doesn't guarantee that the next time it will be a >> boy. >> >> Is there any way to do this? I have been trying to generate a new repeat >> group with only the boys, but I haven't succeeded. The main problem for >> this seems to be that I can not pass on information from one instance to >> the next in a repeat group (from position(..) - 1 to position(..)). With >> this, you could implement any "loop" to solve these kind of problems. >> >> Thanks! >> Wouter >> >> -- >> -- >> Post: opend...@googlegroups.com >> Unsubscribe: opendatakit...@googlegroups.com >> Options: http://groups.google.com/group/opendatakit?hl=en >> >> --- >> You received this message because you are subscribed to the Google Groups >> "ODK Community" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to opendatakit...@googlegroups.com . >> For more options, visit https://groups.google.com/groups/opt_out. >> > >