{"action":"closed","issue":{"url":"https://api.github.com/repos/vega/vega/issues/324","labels_url":"https://api.github.com/repos/vega/vega/issues/324/labels{/name}","comments_url":"https://api.github.com/repos/vega/vega/issues/324/comments","events_url":"https://api.github.com/repos/vega/vega/issues/324/events","html_url":"https://github.com/vega/vega/issues/324","id":99928434,"number":324,"title":"Expression and expression language are not documented","user":{"login":"espinielli","id":891692,"avatar_url":"https://avatars.githubusercontent.com/u/891692?v=3","gravatar_id":"","url":"https://api.github.com/users/espinielli","html_url":"https://github.com/espinielli","followers_url":"https://api.github.com/users/espinielli/followers","following_url":"https://api.github.com/users/espinielli/following{/other_user}","gists_url":"https://api.github.com/users/espinielli/gists{/gist_id}","starred_url":"https://api.github.com/users/espinielli/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/espinielli/subscriptions","organizations_url":"https://api.github.com/users/espinielli/orgs","repos_url":"https://api.github.com/users/espinielli/repos","events_url":"https://api.github.com/users/espinielli/events{/privacy}","received_events_url":"https://api.github.com/users/espinielli/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/vega/vega/labels/documentation","name":"documentation","color":"0b02e1"}],"state":"closed","locked":false,"assignee":null,"milestone":null,"comments":2,"created_at":"2015-08-09T20:53:17Z","updated_at":"2015-08-14T17:34:10Z","closed_at":"2015-08-14T17:34:10Z","body":"(At least) in Data Transform > [Filter](https://github.com/vega/vega/wiki/Data-Transforms#-filter) `Expression` and `expression language` (pointing to `Expression`) are mentioned but no page exists to describe them.\r\n\r\nMy real problem is that what provided in for example ex_jobs.json in the supplementary material to [Reactive Vega](http://idl.cs.washington.edu/papers/reactive-vega) article is no more working/parsing.\r\nIn fact my attempts to transform\r\n\r\n```json\r\n    {\r\n      \"name\": \"jobs\",\r\n      \"source\": \"jobs_source\",\r\n      \"transform\": [\r\n        {\r\n          \"type\": \"filter\", \r\n          \"predicate\": {\r\n            \"type\": \"or\",\r\n            \"operands\": [\r\n              {\"type\": \"==\", \"operands\": [{\"signal\": \"filter_gender\"}, {\"value\": \"all\"}]},\r\n              {\"type\": \"==\", \"operands\": [{\"signal\": \"filter_gender\"}, {\"field\": \"data.sex\"}]}\r\n            ]\r\n          }\r\n        }\r\n```\r\n\r\nto something parsing in Vega 2.0\r\n\r\n```json\r\n  \"signals\": [\r\n    {\r\n      \"name\": \"filter_job\",\r\n      \"init\": {\"value\":\"\"},\r\n      \"stream\": [\r\n        {\"type\": \"#textbox:keyup\", \"expr\": \"this.item.value\"},\r\n        {\"type\": \"area:click\", \"expr\": \"this.datum.data.job\"}\r\n      ]\r\n    },\r\n    {\r\n      \"name\": \"filter_gender\",\r\n      \"init\": {\"value\": \"all\"},\r\n      \"stream\": [\r\n        {\"type\": \"input[name=gender]:click\", \"expr\": \"this.item.value\"}\r\n      ]\r\n    }\r\n  ],\r\n\r\n\r\n  \"data\": [\r\n    {\"name\": \"jobs_source\", \"url\": \"jobs.json\"},\r\n    {\r\n      \"name\": \"jobs\",\r\n      \"source\": \"jobs_source\",\r\n      \"transform\": [\r\n        {\r\n          \"type\": \"filter\", \r\n          \"test\": \"datum.sex == filter_gender\"\r\n        }\r\n```\r\n\r\ndo not result in anything (error or visualization [well I got a black horizontal line for the year but no ticks nor labels...])"}}