问题描述
使用jmespath我想从响应中找到平均值。首先,我需要检查响应是否为空。如果响应不为空,则求平均值。我正在尝试使用此表达式“ [] .points []。value.doubleValue | avg(@)”,但是当响应为空时,表达式将失败。
[
{
"metric": {
"labels": {
"instance_name": "crpsmokes-f4a35bd07"
},"type": "compute.googleapis.com/instance/cpu/utilization"
},"resource": {
"type": "gce_instance","labels": {
"instance_id": "1507883580111256528","project_id": "rightscale.com:resat-prem","zone": "asia-east1-a"
}
},"metricKind": "GAUGE","valueType": "DOUBLE","points": [
{
"interval": {
"startTime": "2020-08-24T22:44:00Z","endTime": "2020-08-24T22:44:00Z"
},"value": {
"doubleValue": 0.00096042153551181288
}
},{
"interval": {
"startTime": "2020-08-24T22:43:00Z","endTime": "2020-08-24T22:43:00Z"
},"value": {
"doubleValue": 0.0019398753629962092
}
},{
"interval": {
"startTime": "2020-08-24T22:42:00Z","endTime": "2020-08-24T22:42:00Z"
},"value": {
"doubleValue": 0.0019628626377153086
}
},{
"interval": {
"startTime": "2020-08-24T22:41:00Z","endTime": "2020-08-24T22:41:00Z"
},"value": {
"doubleValue": 0.0019210491946092627
}
},{
"interval": {
"startTime": "2020-08-24T22:40:00Z","endTime": "2020-08-24T22:40:00Z"
},"value": {
"doubleValue": 0.0018963341116292535
}
},{
"interval": {
"startTime": "2020-08-24T22:39:00Z","endTime": "2020-08-24T22:39:00Z"
},"value": {
"doubleValue": 0.0019406727388149156
}
},{
"interval": {
"startTime": "2020-08-24T22:38:00Z","endTime": "2020-08-24T22:38:00Z"
},"value": {
"doubleValue": 0.0019643314070845481
}
},{
"interval": {
"startTime": "2020-08-24T22:37:00Z","endTime": "2020-08-24T22:37:00Z"
},"value": {
"doubleValue": 0.0019477523878447774
}
},{
"interval": {
"startTime": "2020-08-24T22:36:00Z","endTime": "2020-08-24T22:36:00Z"
},"value": {
"doubleValue": 0.0019031642638339008
}
},{
"interval": {
"startTime": "2020-08-24T22:35:00Z","endTime": "2020-08-24T22:35:00Z"
},"value": {
"doubleValue": 0.0019058478564064766
}
},{
"interval": {
"startTime": "2020-08-24T22:34:00Z","endTime": "2020-08-24T22:34:00Z"
},"value": {
"doubleValue": 0.0019202072242573347
}
},{
"interval": {
"startTime": "2020-08-24T22:33:00Z","endTime": "2020-08-24T22:33:00Z"
},"value": {
"doubleValue": 0.0019225147371779864
}
},{
"interval": {
"startTime": "2020-08-24T22:32:00Z","endTime": "2020-08-24T22:32:00Z"
},"value": {
"doubleValue": 0.0019468938226940699
}
},{
"interval": {
"startTime": "2020-08-24T22:31:00Z","endTime": "2020-08-24T22:31:00Z"
},"value": {
"doubleValue": 0.0018969617509197196
}
},{
"interval": {
"startTime": "2020-08-24T22:30:00Z","endTime": "2020-08-24T22:30:00Z"
},"value": {
"doubleValue": 0.0019062680485175084
}
},{
"interval": {
"startTime": "2020-08-24T22:29:00Z","endTime": "2020-08-24T22:29:00Z"
},"value": {
"doubleValue": 0.0019370667695042699
}
},{
"interval": {
"startTime": "2020-08-24T22:28:00Z","endTime": "2020-08-24T22:28:00Z"
},"value": {
"doubleValue": 0.0020045164017271112
}
},{
"interval": {
"startTime": "2020-08-24T22:27:00Z","endTime": "2020-08-24T22:27:00Z"
},"value": {
"doubleValue": 0.0020103660806600012
}
},{
"interval": {
"startTime": "2020-08-24T22:26:00Z","endTime": "2020-08-24T22:26:00Z"
},"value": {
"doubleValue": 0.0019040336136034359
}
},{
"interval": {
"startTime": "2020-08-24T22:25:00Z","endTime": "2020-08-24T22:25:00Z"
},"value": {
"doubleValue": 0.0019056174446023513
}
},{
"interval": {
"startTime": "2020-08-24T22:24:00Z","endTime": "2020-08-24T22:24:00Z"
},"value": {
"doubleValue": 0.0019463043436514244
}
},{
"interval": {
"startTime": "2020-08-24T22:23:00Z","endTime": "2020-08-24T22:23:00Z"
},"value": {
"doubleValue": 0.0019467681385854972
}
},{
"interval": {
"startTime": "2020-08-24T22:22:00Z","endTime": "2020-08-24T22:22:00Z"
},"value": {
"doubleValue": 0.0019057447090541284
}
},{
"interval": {
"startTime": "2020-08-24T22:21:00Z","endTime": "2020-08-24T22:21:00Z"
},"value": {
"doubleValue": 0.0018988823662930087
}
}]
}
]
解决方法
如果avg
函数收到的内容不是由一个或多个数字组成且仅由数字组成的列表,则会产生错误。您可能要处理三种特殊情况:
- 列表为空。例如。没有指标或指标没有意义。
- 该列表包含非数字。例如。点的
null
或value
中有value.doubleValue
个值。 - 没有列表。例如。整个回复是
null
。
为简单起见,我将假设情况1是其中唯一被认为是正常的情况,但是如果需要,您可以扩展此方法以涵盖其他情况。
这是一个查询,它会导致null
而不是当列表中没有项目时出现错误:
[].points[].value.doubleValue | (@ != `[]`) && avg(@) || `null`
通常,我们可以使用表达式A && B || C
来表示“如果A
为true,则使用B
的值,否则使用C
的值” ,只要B
是类似真值的A
就不会是false value。 (请注意,与其他一些语言不同,在JMESPath中零不被视为错误值。)在我们的表达式中,当列表具有值时,@ != `[]`
为true,而为空时,则为false。因此,如果为true,则将评估&&
的右侧以计算平均值,而为false时,&&
将会短路,而只是false
,而无需尝试计算平均值。最后,|| `null`
将保留平均值计算的值,但将false
替换为null
。