mongodb $regex error: unknown operator

Question

I'm trying to check the 1st character of a field to not be a-z

db.zips.aggregate( 
 [
{ $group : { city: { $regex: '^[a-z]', $options: 'i' }, n : {$sum:1} } }
 ]
)

Here is a sample doc expected to be found but the query errors with unknown operator '$regex'. MongoDB v2.4.5 is installed:

{"city": "25536", "loc": [-82.076761, 38.087553], "pop": 61, "state": "WV", "_id":   "25536"}

Error:

Error: Printing Stack Trace
at printStackTrace (src/mongo/shell/utils.js:37:15)
at DBCollection.aggregate (src/mongo/shell/collection.js:897:9)
at (shell):1:9
Wed Jul 31 12:14:14.737 JavaScript execution failed: aggregate failed: {
    "errmsg" : "exception: unknown group operator '$regex'",
    "code" : 15952,
    "ok" : 0
} at src/mongo/shell/collection.js:L898

Thanks!

P.S. I tried this also:

db.zips.aggregate( 
[
{ $project : { city: /^[a-z]/i }}
,{ $group : { city : "$city", n : {$sum:1} } }
]
)

Error: Printing Stack Trace
at printStackTrace (src/mongo/shell/utils.js:37:15)
at DBCollection.aggregate (src/mongo/shell/collection.js:897:9)
at (shell):1:9
Wed Jul 31 12:26:21.531 JavaScript execution failed: aggregate failed: {
    "errmsg" : "exception: disallowed field type RegEx in object expression
(at 'city')",
    "code" : 15992,
    "ok" : 0
} at src/mongo/shell/collection.js:L898

So appears that the ways I'm trying to use regex is incorrect or in the incorrect places/operations.

Community · Accepted Answer · 2017-05-23 10:27:08Z

2

$regex cannot be used there, you want to watch a JIRA like this: https://jira.mongodb.org/browse/SERVER-8892

However, I think you actually want to $match by the regex instead of group. So you want to match all cities in your criteria and then you wanna group them.

As reference here is a duplicate question I just found by Googling: using $regex in mongodb aggregation framework in $group

edited May 23, 2017 at 10:27

CommunityBot

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answered Jul 31, 2013 at 17:24

Sammaye

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1 Comment

Will Lopez Over a year ago

Thanks! I saw that one but couldn't get anything working so I wanted to focus on $regex but I see it won't work they way I'm trying to use it.

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