In one embodiment, a method includes receiving event information associated with an event listing, the event information being inputted by a user of an online event management system at a client device; transmitting the event information to the online event management system, the event listing being synchronously categorized with the sending of the event information; and receiving from the online event management system one or more categories associated with the event listing for display to the user at the client device, the categories being automatically determined based on categorization models of the online event management system in response to the transmitted event information.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method comprising: receiving, at a client device, event information associated with an event listing, the event information being inputted by a user of an online event management system at the client device; transmitting, to the online event management system, the event information associated with the event listing, the event listing being synchronously categorized with the sending of the event information; and receiving, at the client device from the online event management system, one or more categories associated with the event listing for display to the user, the one or more categories being automatically determined based on one or more categorization models of the online event management system in response to the transmitted event information. 2. The method of claim 1, wherein the event information is inputted by the user on a webpage hosted by the online event management system. 3. The method of claim 1, wherein the event information is inputted by the user in an application associated with the online event management system. 4. The method of claim 1, wherein the one or more categories are displayed on a webpage for creating the event listing hosted by the online event management system, the one or more categories being displayed automatically in response to the event information being inputted by the user. 5. The method of claim 1, further comprising: receiving, at the client device, one or more user-identified categories associated with the event listing, and wherein the one or more categories are automatically determined further based on the one or more user-identified categories. 6. The method of claim 1, further comprising: calculating, at the online event management system, one or more category probabilities for the event listing using one or more categorization models, respectively, each categorization model calculating a category probability based at least in part on the event information associated with the event listing, each category probability corresponding to a category, the category probability being equal to the probability that the event listing falls within the category; and for each category probability greater than or equal to a threshold probability, associating with the event listing the category corresponding to the category probability. 7. The method of claim 6, wherein each categorization model includes one or more variables based on: a preset list of one or more features; or a list of one or more values of features being associated with the event listing. 8. The method of claim 1, wherein one or more categorization models are refined by one or more learning algorithms, the learning algorithms being logistic regression, binary classification, multiclass classification, or maximum likelihood estimation. 9. The method of claim 1, wherein: the event information identifies one or more of: a title of the event; a description of the event; a self-identified category of the event; a derived category of the event; a keyword of the event; an instructions for the event; an attendee of the event; an organizer of the event; a venue of the event; a ticket type of the event; a ticket price of the event; or a geographic location of the event; and calculating the one or more category probabilities is further based at least in part on one or more of: the title of the event; the description of the event; the self-identified category of the event; the derived category of the event; the keyword of the event; the instructions for the event; the attendee of the event; the organizer of the event; the venue of the event; the ticket type of the event; the ticket price of the event; or the geographic location of the event. 10. The method of claim 1, wherein the category probability for the event listing is a percentile rank equal to the percentage of event listings that have a category probability the same or lower than the event listing. 11. The method of claim 1, wherein calculating the category probability based at least in part on the event information associated with the event listing comprises: accessing a list comprising a plurality of features; comparing the list to the event information; for each feature present in the event information, calculating a value for the feature; and calculating the category probability based at least in part on one or more of the values of the features. 12. The method of claim 11, wherein calculating the category probability based at least in part on the event information associated with the event listing further comprises: for each feature not present in the event information, calculating a value of for the feature equal to zero. 13. The method of claim 11, wherein the features present in the event information are represented as a matrix. 14. The method of claim 11, calculating the one or more category c probabilities fc(z) wherein: f c  ( z ) = 1 1 + e - z ; and z=β0+β1x1+β2x2+ . . . +βkxk, wherein z is the result of a comparison between a set of features associated with an event listing and the weights associated with those features, β is a factor associated with a particular feature, and x is an indication of a particular feature in the event listing. 15. The method of claim 11, wherein the list comprising a plurality of features is determined by a method comprising: accessing D training event informations, each training event information being associated with a training event listing; calculating a term frequency for each term i in the D training event informations; and for each term i with a term frequency greater than or equal to a threshold term frequency, categorizing the term as a feature. 16. The method of claim 15, wherein the term frequency for each term i in the D training event informations equals (tf-idf)i,j, wherein: (tf=idf)i,j=tfi,j×idfi; tf i , j = n ij ∑ k   n k , j , wherein tfi,j is the term frequency of term i in document j, ni,j is the number of times term i appears in document j, and k is the total number of terms; and idf i = log   D   { d  :   t i ∈ d }  , wherein idfi is the inverse document frequency of term i, and d is the current document. 17. An apparatus comprising: one or more processors; and a memory coupled to the processors comprising instructions executable by the processors, the processors operable when executing the instructions to: receive, at a client device, event information associated with an event listing, the event information being inputted by a user of an online event management system at the client device; transmit, to the online event management system, the event information associated with the event listing, the event listing being synchronously categorized with the sending of the event information; and receive, at the client device from the online event management system, one or more categories associated with the event listing for display to the user, the one or more categories being automatically determined based on one or more categorization models of the online event management system in response to the transmitted event information. 18. One or more computer-readable non-transitory storage media embodying instructions that are operable when executed to: receive, at a client device, event information associated with an event listing, the event information being inputted by a user of an online event management system at the client device; transmit, to the online event management system, the event information associated with the event listing, the event listing being synchronously categorized with the sending of the event information; and receive, at the client device from the online event management system, one or more categories associated with the event listing for display to the user, the one or more categories being automatically determined based on one or more categorization models of the online event management system in response to the transmitted event information.