I have a simple question (or so I thought).
I have a dictionary, lets say it looks like this:
dict = {'A':100, 'a':10, 'T':50, 't':5}
I simply want to delete the key with the highest value. I tried this:
del max(dict.values())
and this is the error message: 'Syntax Error: can´t delete function call'.
I want the end result to be:
dict = {'a':10, 'T':50, 't':5}
You need to get a hold of the key to the max value.
Try this instead:
del d[max(d, key=d.get)]
Also, you should avoid calling your variable dict because it shadows the built-in name.
max(d.values()) will give you the maximum value (100), but to delete an entry from a dictionary you need the corresponding key ('A').
You can do this:
d = {'A':100, 'a':10, 'T':50, 't':5}
key_to_delete = max(d, key=lambda k: d[k])
del d[key_to_delete]
By the way, you shouldn't name your dictionary dict because that's the name of a built-in type.
If there may be multiple entries with the same maximum value and you want to delete all of them:
val_to_delete = max(d.values())
keys_to_delete = [k for k,v in d.iteritems() if v==val_to_delete]
for k in keys_to_delete:
del d[k]
Related
I am looking to solve a problem to compare the string of the key and value of the same dictionary.
To return a dictionary of all key and values where the value contains the key name as a substring.
a = {"ant":"antler", "bi":"bicycle", "cat":"animal"}
the code needs to return the result:
b = {"ant":"antler", "bi":"bi cycle"}
You can iterate through the dictionary and unpack the key and the value at the same time this way:
b = {}
for key, value in a.items():
if value in key:
b[value] = key
This will generate your wanted solution. It does that by unpacking both the key and the value and checking if they match afterward.
You can also shorten that code by using a dictionary comprehension:
b = {key:value for key, value in a.items() if key in value}
This short line does the exact same thing as the code before. It even uses the same functionalities with only one addition - a dictionary comprehension. That allows you to put all that code in one simple line and declare the dictionary on the go.
answer = {k:v for k,v in a.items() if k in v}
Notes:
to iterate over key: value pair we use dict.items();
to check if a string is inside some other string we use in operator;
to filter items we use if-clause in the dictionary comprehension.
See also:
about dictionary comprehensions
about operators in and not in
d={1:'a', 2:'b', 3:'c', 4:'a', 5:'d', 6:'e', 7:'a', 8:'b'}
value = raw_input("Choose a value to be searched: ")
data = ""
if value in d:
data = d.keys["value"]
print(data)
else:
print "There isn't such value in the dictionary"
So I write 'a' and I want to get the key '1'
but it skips "data = d.keys["value"] print(data)" and it prints me the message of "else"
What have I done wrong?
Containment checks for dict check the keys, not the values, and 'a' is a value in the dict, not a key.
The simplest fix would be to change your test to:
if value in d.viewvalues(): # d.values() on Python 3
but that's still sub-optimal; you can't perform efficient (O(1)) lookups in the values of a dict (nor can you do d.keys[value] as you seem to think you can; you'd have to perform a second linear scan to find the key, or perform a more complicated single scan to determine if the value exists and pull the key at the same time).
Really though, it seems like you want your dictionary reversed, with the keys as values and vice-versa. Doing it this way:
d = {1:'a', 2:'b', 3:'c', 4:'a', 5:'d', 6:'e', 7:'a', 8:'b'}
d_inv = {v: k for k, v in d.items()} # Make inverted version of d
value = raw_input("Choose a value to be searched: ")
if value in d_inv:
data = d_inv[value]
print(data)
else:
print "There isn't such value in the dictionary"
you can perform the containment check and lookup efficiently (if d isn't otherwise needed, you can just replace d with the same structure as d_inv and use d instead of d_inv uniformly).
As stated, you need the value, here's an alternative
if any(d[value] for value in d):
Then, d.keys["value"] is actually d[value]
You could do something like this:
d={1:'a', 2:'b', 3:'c', 4:'a', 5:'d', 6:'e', 7:'a', 8:'b'}
value = 'q'
data = [key for key, val in d.items() if val == value]
if len(data) > 0:
print(data)
else:
print "There isn't such value in the dictionary"
Then you would get the results
[1, 4, 7]
I had the following dictionary:
ref_range = range(0,100)
aas = list("ACDEFGHIKLMNPQRSTVWXY*")
new_dict = {}
new_dict = new_dict.fromkeys(ref_range,{k:0 for k in aas})
Then I added a 1 to a specific key
new_dict[30]['G'] += 1
>>>new_dict[30]['G']
1
but
>>>new_dict[31]['G']
1
What is going on here? I only incremented the nested key 30, 'G' by one.
Note: If I generate the dictionary this way:
new_dict = {}
for i in ref_range:
new_dict[i] = {a:0 for a in aas}
Everything behaves fine. I think this is a similar question here, but I wanted to know a bit about why this happening rather than how to solve it.
fromkeys(S, v) sets all of the keys in S to the same value v. Meaning that all of the keys in your dictionary new_dict refer to the same dictionary object, not to their own copies of that dictionary.
To set each to a different dict object you cannot use fromkeys. You need to just set each key to a new dict in a loop.
Besides what you have you could also do
{i: {a: 0 for a in aas} for i in ref_range}
Essentially I want to delete every key in a dictionary if its value doesn't equal the highest value.
Let's say this is the dictionary:
myDict = {"Bob": 1, "Bill": 5, "Barry": 4, "Steve": 5}
I'm able to sort it by value using this:
myDict = sorted(myDict, key=myDict.get, reverse=True)
Now I want to remove any key in the dictionary that doesn't equal the highest value (in this case '5'). To end up with this:
myDict = {"Bill": 5, "Steve": 5}
I've tried using this for loop:
for item, v in myDict:
if v < myDict[0]:
del myDict[v]
But I get this error:
ValueError: too many values to unpack (expected 2)
This is a) my first time posting here, and b) I've only been learning Python for a few months so I'm sorry if I've made any stupid mistakes.
for item, v in myDict just give you keys mydict, and you are collecting that key in item, v that's why,
use myDict.items() or myDict.iteritems().
for item, v in myDict.iteritems():
if v < myDict[0]:
del myDict[v]
To get Highest value of myDict
max(myDict.values())
To delete keys from Dict never change the iterator you are iterating on, it will give you RuntimeError. So copy it in another variable and change previous one as Anand S Kumar suggested.
You should never alter the object you're iterating over, that usually yields unexpected results (internal pointers get shifted and you miss elements in your iteration and such). You best gather the keys you want to delete and then remove the keys in a separate iteration:
keys = [k for k in myDict.keys() if myDict[k] == max(myDict.values())];
for k in keys: del myDict[k];
It might be best to put the max expression in a variable too so it doesn't get evaluated multiple times. Not sure if Python's able to optimize that for you (probably not).
You can use dictionary comprehension to create a new dictionary:
newDict = {k: v for k,v in myDict.items() if v == max(myDict.values())}
The output for newDict:
{'Steve': 5, 'Bill': 5}
I have a dictionary like this:
dct = {'one': 'value',
'two': ['value1','value2','value1'],
'three':['otherValue1','otherValue2','otherValue1'],
'dontCareAboutThisKey':'debug'}
I need to remove duplicate values from the lists. I wrote a function to do this:
no_dups = {}
for keys in dct:
if isinstance(dct[keys], list) and keys != 'dontCareAboutThisKey':
for value in dct[keys]:
if value not in no_dups.values():
no_dups[keys].append(value)
else:
no_dups[keys] = dct[keys]
I'm checking if value of the current key is a list. If no, it just 'copy' key to no_dups dictionary. If it is a list and not a key that I don't care about (there are no duplicates for sure) - it should check if current value already exists in no_dups.values() and append it to current key. Problem is that I'm getting an error:
KeyError: 'two:'
I know it's because I'm trying to add a value to non existing key but I have no idea how to deal with this and make it work.
I think the best way to deal with adding the key and appending at the same time is with dicts' setdefault() method:
no_dups.setdefault(keys,[]).append(value)
But rather than that, you can do this in a more neat way like this:
#remove duplicates
no_dups = {k:list(set(v)) if isinstance(v, list) and k != 'dontCareAboutThisKey' else v
for k,v in dct.items()} # or dct.iteritems() if using python2.x
That hack will, for key value combinations that pass the if test, convert the list into a set (removing duplicates) and then in a list again. For other key value combinations it will leave it intact.
dct = {'one': 'value',
'two': ['value1','value2','value1'],
'three':['otherValue1','otherValue2','otherValue1'],
'dontCareAboutThisKey':'debug'}
set(dct) returns a set, which is a list without duplicates:
for key, value in dct.items():
if not isinstance(value, basestring):
dct[key] = set(value)
If you need a new dictionary you could do:
new_dct = {}
for key, value in dct.items():
if not isinstance(value, basestring):
new_dct[key] = set(value)
else:
new_dct[key] = value
If You want to remove duplicates, just change You list to set, with set() function:
https://docs.python.org/2/tutorial/datastructures.html#sets
It automatically gives You unique set, then You can always change it back to list.