How can I replace a nested for loop with recursion?
Question:
First of all, I’m still a newb to python so please take it easy on me.
I’ve done my research and I have a basic understanding of how to write a recursive function, but I’m totally confused at the task ahead of me.
I would really like some tips and pointers so I can do this myself to really understand.
Here’s the task:
- Iterate through a dictionary
- check if there is a ‘children’ key
- if true, do something
- repeat
Here’s the issue,
The ‘option’ key is nested in another key called ‘children’. There for I would like to iterate through each ‘children’ key until they exist no more.
Here’s what the code looks like without recursion. Of course it fails because its too explicate, too rigid.
#level(one/two/three) refer to the level of nesting, easier for me to know where I am in the loop.
#qdf_v2 is a particular type of file which is essentially a dictionary
for levelone in qdf_v2['children']:
if 'children' in levelone:
store = options
for leveltwo in levelone['children']:
if 'children' in leveltwo:
store = options
for levelthree in leveltwo['children']:
if 'children' in levellevel:
repeat....
I would like to loop through the dictionary and it’s ‘children’ key until they don’t exist anymore.
Here’s some JSON you can copy and past this in http://www.jsoneditoronline.org/ to see what I’m working with.
{
"base": "http://panoptic-fearless.ldc.yougov.net/questionnaires/Test_maj_demo_newG4_2/versions/12/",
"children": [
{
"name": "one",
"children": [
{
"name": "measures",
"children": [
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "How much would you say you like or dislike P.E. at school? ",
"name": "KYS_Q1",
"responses": {
"items": [
{
"code": 1,
"text": "I love it",
"element": "qdf:response"
},
{
"code": 2,
"text": "I like it",
"element": "qdf:response"
},
{
"code": 3,
"text": "I don’t like it",
"element": "qdf:response"
},
{
"code": 4,
"text": "I hate it",
"element": "qdf:response"
},
{
"code": 5,
"text": "Don’t know",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q1"
}
]
},
{
"children": [
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "4",
"chart_type": "pie",
"chart_color": "pink"
},
"text": "{multiple order="randomize" max=3} You said that you $event P.E. at school...<br/> Which THREE of the following are your MAIN reasons for not liking P.E. at school? (Please tick up to three options)",
"name": "KYS_Q2",
"responses": {
"items": [
{
"code": 1,
"text": "I don't like going outside in bad weather (e.g. in the cold, rain etc.)",
"element": "qdf:response"
},
{
"code": 2,
"text": "I’m always picked last to join a team",
"element": "qdf:response"
},
{
"code": 3,
"text": "I don't like my P.E. teacher/ don’t think they are very good",
"element": "qdf:response"
},
{
"code": 4,
"text": "I’m not very good at it",
"element": "qdf:response"
},
{
"code": 5,
"text": "I find the games/ sports we play boring",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q2"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "line",
"chart_color": "green"
},
"text": "{multiple order="randomize"} Below are some feelings that people can have about doing P.E. at school...<br/> Which of the following words describe how you feel about doing P.E. at school? (Please tick all that apply) ",
"name": "KYS_Q3A",
"responses": {
"items": [
{
"code": 1,
"text": "Stressed",
"element": "qdf:response"
},
{
"code": 2,
"text": "Scared",
"element": "qdf:response"
},
{
"code": 3,
"text": "Worried",
"element": "qdf:response"
},
{
"code": 4,
"text": "Sick",
"element": "qdf:response"
},
{
"code": 5,
"text": "Tiring ",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q3A"
}
]
}
],
"element": "qdf:section"
},
{
"type": "single",
"options": {
"sort_order": "desending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{single order="randomize"} You said that you $event P.E...<br/> Which ONE of the following is the main reason you like it? ",
"name": "KYS_Q4",
"responses": {
"items": [
{
"code": 1,
"text": "I like getting outside/ not being in the classroom",
"element": "qdf:response"
},
{
"code": 2,
"text": "I like my P.E. teacher",
"element": "qdf:response"
},
{
"code": 3,
"text": "I’m good at it",
"element": "qdf:response"
},
{
"code": 4,
"text": "I find the games/ sports fun",
"element": "qdf:response"
},
{
"code": 5,
"text": "I find the games/ sports easy",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q4"
}
]
}
],
"element": "qdf:page"
}
],
"element": "qdf:module"
},
{
"name": "two",
"children": [
{
"name": "test",
"children": [
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{multiple order="randomize"}Below are some feelings that people can have about doing P.E at school...<br/> Which of the following words describe how you feel about doing P.E. at school? (Please tick all that apply) ",
"name": "KYS_Q5A",
"responses": {
"items": [
{
"code": 1,
"text": "Energised/ Awake",
"element": "qdf:response"
},
{
"code": 2,
"text": "Excited",
"element": "qdf:response"
},
{
"code": 3,
"text": "Relaxed",
"element": "qdf:response"
},
{
"code": 4,
"text": "Confident",
"element": "qdf:response"
},
{
"code": 5,
"text": "Happy",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q5A"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "25",
"chart_type": "column",
"chart_color": "orange"
},
"text": "{multiple order="randomize"} For the following question please do not be afraid to be as honest as possible, no one else will be told your personal answers. <br/> Which of the following have you EVER done in order to avoid taking part in P.E. at school? (Please tick all that apply) ",
"name": "KYS_Q6",
"responses": {
"items": [
{
"code": 1,
"text": "Lied about forgetting my kit",
"element": "qdf:response"
},
{
"code": 2,
"text": "Lied about an injury",
"element": "qdf:response"
},
{
"code": 3,
"text": "Lied about feeling unwell",
"element": "qdf:response"
},
{
"code": 4,
"text": "Faked a note from my parents/ guardian",
"element": "qdf:response"
},
{
"code": 5,
"text": "Faked a note from my doctor/ health professional",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q6"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{multiple order="randomize"} For the following question, please think about the teacher who has taught you P.E. MOST recently and if you have more than one teacher teaching you P.E. please think about the one who has taught you most often. <br/> Which of the following statements do you agree with? (Please tick all that apply)",
"name": "KYS_Q7",
"responses": {
"items": [
{
"code": 1,
"text": "My P.E. teacher inspires me to do more exercise",
"element": "qdf:response"
},
{
"code": 2,
"text": "My P.E. teacher motivates me to take part in P.E. lessons",
"element": "qdf:response"
},
{
"code": 3,
"text": "My P.E. teacher scares me",
"element": "qdf:response"
},
{
"code": 4,
"text": "My P.E. teacher makes P.E. boring",
"element": "qdf:response"
},
{
"code": 5,
"text": "My P.E. teacher makes P.E. fun",
"element": "qdf:response"
},
{
"code": 6,
"text": "My P.E. teacher makes P.E. difficult/ hard",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q7"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{multiple order="randomize"} What would make you like P.E. more? (Please tick all that apply)",
"name": "KYS_Q8",
"responses": {
"items": [
{
"code": 1,
"text": "If the P.E. teacher was nicer to me",
"element": "qdf:response"
},
{
"code": 2,
"text": "If more lessons took place indoors (e.g. in the sports hall or a gym)",
"element": "qdf:response"
},
{
"code": 3,
"text": "If more lessons took place outdoors",
"element": "qdf:response"
},
{
"code": 4,
"text": "If we did more interesting sports/ activities",
"element": "qdf:response"
},
{
"code": 5,
"text": "If we had more choice of the types of sport we had to do",
"element": "qdf:response"
},
{
"code": 6,
"text": "If we could wear what we wanted for the lesson",
"element": "qdf:response"
},
{
"options": {
"fixed": true
},
"children": [
{
"export": [
{
"name": "KYS_Q8other"
}
],
"name": "KYS_Q8other",
"type": "open",
"element": "qdf:question"
}
],
"code": 7,
"text": "Other ",
"element": "qdf:response"
},
{
"options": {
"xor": true,
"fixed": true
},
"code": 8,
"text": "Don’t know",
"element": "qdf:response"
},
{
"options": {
"xor": true,
"fixed": true
},
"code": 9,
"text": "Not applicable – nothing would make me like P.E. more than I already do",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q8"
}
]
}
],
"element": "qdf:page"
}
],
"element": "qdf:module"
},
{
"children": [
{
"children": [
{
"text": "n",
"element": "qdf:text"
}
],
"element": "qdf:page"
}
],
"element": "qdf:module"
}
],
"panelid": 13,
"created": "#2014-01-10T15:57:18.594000+00:00#",
"typespec": {
"src": "/questionnaires/typespecs/initial.qdf",
"element": "qdf:typespec"
},
"qdf-ext:ext": [
"meaningful-page-names"
],
"element": "qdf:questionnaire",
"builtin": {
"src": "/questionnaires/builtins/initial.qdf",
"element": "qdf:typedef"
},
"committer": "majeed.sahebzadha",
"name": "Test_maj_demo_newG4_2",
"commit message": "added a new module within a module"
}
Answers:
def recurseDict(dictionary):
if "children" in dictionary:
return recurseDict(dictionary['children'])
else:
return "Whatever you want to return here -- you didn't specify"
This will take a dictionary, check if "children" is one of its keys, then recurse through the dictionary dictionary['children'] and etc etc until it gets to a point where there isn’t a 'children' key (e.g. the dictionary has no further branches) where it goes into the else branch and you can return whatever the heck you want — you didn’t specify.
Here is an example approach to recursively go through a dictionary, assuming that each child is also a dictionary:
def compute(my_dict):
if 'children' in my_dict:
print my_dict['children']
for child in my_dict['children']:
compute(child)
I would approach this as follows:
def recursive(input, output=None):
if output is None:
output = {} # container to store results
if 'children' in input:
# do whatever, add things to output
recursive(input['children'], output)
return output
This way, the output dictionary is accessible to all depths of iteration and gets returned with all contents at the end. This means that you don’t have to explicitly deal with the return values of the recursive calls.
Depending on exactly what you have, it may look more like:
def recursive(input, output=None):
if output is None:
output = {} # container to store results
if 'children' in input:
for child in input['children']:
# do whatever, add things to output
recursive(child, output)
return output
And output may be a different container (e.g. list, set).
First of all, I’m still a newb to python so please take it easy on me.
I’ve done my research and I have a basic understanding of how to write a recursive function, but I’m totally confused at the task ahead of me.
I would really like some tips and pointers so I can do this myself to really understand.
Here’s the task:
- Iterate through a dictionary
- check if there is a ‘children’ key
- if true, do something
- repeat
Here’s the issue,
The ‘option’ key is nested in another key called ‘children’. There for I would like to iterate through each ‘children’ key until they exist no more.
Here’s what the code looks like without recursion. Of course it fails because its too explicate, too rigid.
#level(one/two/three) refer to the level of nesting, easier for me to know where I am in the loop.
#qdf_v2 is a particular type of file which is essentially a dictionary
for levelone in qdf_v2['children']:
if 'children' in levelone:
store = options
for leveltwo in levelone['children']:
if 'children' in leveltwo:
store = options
for levelthree in leveltwo['children']:
if 'children' in levellevel:
repeat....
I would like to loop through the dictionary and it’s ‘children’ key until they don’t exist anymore.
Here’s some JSON you can copy and past this in http://www.jsoneditoronline.org/ to see what I’m working with.
{
"base": "http://panoptic-fearless.ldc.yougov.net/questionnaires/Test_maj_demo_newG4_2/versions/12/",
"children": [
{
"name": "one",
"children": [
{
"name": "measures",
"children": [
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "How much would you say you like or dislike P.E. at school? ",
"name": "KYS_Q1",
"responses": {
"items": [
{
"code": 1,
"text": "I love it",
"element": "qdf:response"
},
{
"code": 2,
"text": "I like it",
"element": "qdf:response"
},
{
"code": 3,
"text": "I don’t like it",
"element": "qdf:response"
},
{
"code": 4,
"text": "I hate it",
"element": "qdf:response"
},
{
"code": 5,
"text": "Don’t know",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q1"
}
]
},
{
"children": [
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "4",
"chart_type": "pie",
"chart_color": "pink"
},
"text": "{multiple order="randomize" max=3} You said that you $event P.E. at school...<br/> Which THREE of the following are your MAIN reasons for not liking P.E. at school? (Please tick up to three options)",
"name": "KYS_Q2",
"responses": {
"items": [
{
"code": 1,
"text": "I don't like going outside in bad weather (e.g. in the cold, rain etc.)",
"element": "qdf:response"
},
{
"code": 2,
"text": "I’m always picked last to join a team",
"element": "qdf:response"
},
{
"code": 3,
"text": "I don't like my P.E. teacher/ don’t think they are very good",
"element": "qdf:response"
},
{
"code": 4,
"text": "I’m not very good at it",
"element": "qdf:response"
},
{
"code": 5,
"text": "I find the games/ sports we play boring",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q2"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "line",
"chart_color": "green"
},
"text": "{multiple order="randomize"} Below are some feelings that people can have about doing P.E. at school...<br/> Which of the following words describe how you feel about doing P.E. at school? (Please tick all that apply) ",
"name": "KYS_Q3A",
"responses": {
"items": [
{
"code": 1,
"text": "Stressed",
"element": "qdf:response"
},
{
"code": 2,
"text": "Scared",
"element": "qdf:response"
},
{
"code": 3,
"text": "Worried",
"element": "qdf:response"
},
{
"code": 4,
"text": "Sick",
"element": "qdf:response"
},
{
"code": 5,
"text": "Tiring ",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q3A"
}
]
}
],
"element": "qdf:section"
},
{
"type": "single",
"options": {
"sort_order": "desending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{single order="randomize"} You said that you $event P.E...<br/> Which ONE of the following is the main reason you like it? ",
"name": "KYS_Q4",
"responses": {
"items": [
{
"code": 1,
"text": "I like getting outside/ not being in the classroom",
"element": "qdf:response"
},
{
"code": 2,
"text": "I like my P.E. teacher",
"element": "qdf:response"
},
{
"code": 3,
"text": "I’m good at it",
"element": "qdf:response"
},
{
"code": 4,
"text": "I find the games/ sports fun",
"element": "qdf:response"
},
{
"code": 5,
"text": "I find the games/ sports easy",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q4"
}
]
}
],
"element": "qdf:page"
}
],
"element": "qdf:module"
},
{
"name": "two",
"children": [
{
"name": "test",
"children": [
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{multiple order="randomize"}Below are some feelings that people can have about doing P.E at school...<br/> Which of the following words describe how you feel about doing P.E. at school? (Please tick all that apply) ",
"name": "KYS_Q5A",
"responses": {
"items": [
{
"code": 1,
"text": "Energised/ Awake",
"element": "qdf:response"
},
{
"code": 2,
"text": "Excited",
"element": "qdf:response"
},
{
"code": 3,
"text": "Relaxed",
"element": "qdf:response"
},
{
"code": 4,
"text": "Confident",
"element": "qdf:response"
},
{
"code": 5,
"text": "Happy",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q5A"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "25",
"chart_type": "column",
"chart_color": "orange"
},
"text": "{multiple order="randomize"} For the following question please do not be afraid to be as honest as possible, no one else will be told your personal answers. <br/> Which of the following have you EVER done in order to avoid taking part in P.E. at school? (Please tick all that apply) ",
"name": "KYS_Q6",
"responses": {
"items": [
{
"code": 1,
"text": "Lied about forgetting my kit",
"element": "qdf:response"
},
{
"code": 2,
"text": "Lied about an injury",
"element": "qdf:response"
},
{
"code": 3,
"text": "Lied about feeling unwell",
"element": "qdf:response"
},
{
"code": 4,
"text": "Faked a note from my parents/ guardian",
"element": "qdf:response"
},
{
"code": 5,
"text": "Faked a note from my doctor/ health professional",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q6"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{multiple order="randomize"} For the following question, please think about the teacher who has taught you P.E. MOST recently and if you have more than one teacher teaching you P.E. please think about the one who has taught you most often. <br/> Which of the following statements do you agree with? (Please tick all that apply)",
"name": "KYS_Q7",
"responses": {
"items": [
{
"code": 1,
"text": "My P.E. teacher inspires me to do more exercise",
"element": "qdf:response"
},
{
"code": 2,
"text": "My P.E. teacher motivates me to take part in P.E. lessons",
"element": "qdf:response"
},
{
"code": 3,
"text": "My P.E. teacher scares me",
"element": "qdf:response"
},
{
"code": 4,
"text": "My P.E. teacher makes P.E. boring",
"element": "qdf:response"
},
{
"code": 5,
"text": "My P.E. teacher makes P.E. fun",
"element": "qdf:response"
},
{
"code": 6,
"text": "My P.E. teacher makes P.E. difficult/ hard",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q7"
}
]
},
{
"type": "single",
"options": {
"sort_order": "asending",
"chart_layout": "5",
"chart_type": "bar",
"chart_color": "green"
},
"text": "{multiple order="randomize"} What would make you like P.E. more? (Please tick all that apply)",
"name": "KYS_Q8",
"responses": {
"items": [
{
"code": 1,
"text": "If the P.E. teacher was nicer to me",
"element": "qdf:response"
},
{
"code": 2,
"text": "If more lessons took place indoors (e.g. in the sports hall or a gym)",
"element": "qdf:response"
},
{
"code": 3,
"text": "If more lessons took place outdoors",
"element": "qdf:response"
},
{
"code": 4,
"text": "If we did more interesting sports/ activities",
"element": "qdf:response"
},
{
"code": 5,
"text": "If we had more choice of the types of sport we had to do",
"element": "qdf:response"
},
{
"code": 6,
"text": "If we could wear what we wanted for the lesson",
"element": "qdf:response"
},
{
"options": {
"fixed": true
},
"children": [
{
"export": [
{
"name": "KYS_Q8other"
}
],
"name": "KYS_Q8other",
"type": "open",
"element": "qdf:question"
}
],
"code": 7,
"text": "Other ",
"element": "qdf:response"
},
{
"options": {
"xor": true,
"fixed": true
},
"code": 8,
"text": "Don’t know",
"element": "qdf:response"
},
{
"options": {
"xor": true,
"fixed": true
},
"code": 9,
"text": "Not applicable – nothing would make me like P.E. more than I already do",
"element": "qdf:response"
}
],
"element": "qdf:response_group"
},
"element": "qdf:question",
"export": [
{
"name": "KYS_Q8"
}
]
}
],
"element": "qdf:page"
}
],
"element": "qdf:module"
},
{
"children": [
{
"children": [
{
"text": "n",
"element": "qdf:text"
}
],
"element": "qdf:page"
}
],
"element": "qdf:module"
}
],
"panelid": 13,
"created": "#2014-01-10T15:57:18.594000+00:00#",
"typespec": {
"src": "/questionnaires/typespecs/initial.qdf",
"element": "qdf:typespec"
},
"qdf-ext:ext": [
"meaningful-page-names"
],
"element": "qdf:questionnaire",
"builtin": {
"src": "/questionnaires/builtins/initial.qdf",
"element": "qdf:typedef"
},
"committer": "majeed.sahebzadha",
"name": "Test_maj_demo_newG4_2",
"commit message": "added a new module within a module"
}
def recurseDict(dictionary):
if "children" in dictionary:
return recurseDict(dictionary['children'])
else:
return "Whatever you want to return here -- you didn't specify"
This will take a dictionary, check if "children" is one of its keys, then recurse through the dictionary dictionary['children'] and etc etc until it gets to a point where there isn’t a 'children' key (e.g. the dictionary has no further branches) where it goes into the else branch and you can return whatever the heck you want — you didn’t specify.
Here is an example approach to recursively go through a dictionary, assuming that each child is also a dictionary:
def compute(my_dict):
if 'children' in my_dict:
print my_dict['children']
for child in my_dict['children']:
compute(child)
I would approach this as follows:
def recursive(input, output=None):
if output is None:
output = {} # container to store results
if 'children' in input:
# do whatever, add things to output
recursive(input['children'], output)
return output
This way, the output dictionary is accessible to all depths of iteration and gets returned with all contents at the end. This means that you don’t have to explicitly deal with the return values of the recursive calls.
Depending on exactly what you have, it may look more like:
def recursive(input, output=None):
if output is None:
output = {} # container to store results
if 'children' in input:
for child in input['children']:
# do whatever, add things to output
recursive(child, output)
return output
And output may be a different container (e.g. list, set).