jq：计算满足条件的嵌套对象的值 [英] jq: count nest object values which satisfy condition

问题描述

json数据：

{testId: '1' studentId:{'s1':{score: 20} 's2':{score: 80}}}
{testId: '2' studentId:{'s1':{score: 60} 's2':{score: 70}}}
{testId: '3' studentId:{'s5':{score: 40} 's7':{score: 30}}}
...

我想用JQ告诉我，有多少学生在每次考试中得分> x。

I would like to use JQ to tell me how many students achieved a score > x, for each test.

上面的输入，x = 50，则输出：

Thus for the above input and x = 50, the output:

{testId: '1' numStudents:1}
{testId: '2' numStudents:2}
{testId: '3' numStudents:0}

我能够生成所有在每次考试中达到50分以上的学生的列表，

I am able to generate a list of all students who achieved > 50 on each test with

{testId, studentId: .studentId[]?} | select(.studentId.score>50)

此命令创建一个对象列表，其中每个对象都包含testId ，studentId和score，所有分数均大于50。但是，我不知道如何将这些结果重新组合到所需的输出中。

This command creates a list of objects where each object contains testId, studentId and score, where all scores are greater than 50. However I do not know how to recombine these results into the output I want.

推荐答案

以下内容假设输入包含有效的JSON对象流。

The following assumes the input consists of a stream of valid JSON objects.

一种方法是使用 add ：

$ jq '{testId, numStudents: ([select(.studentId[].score > 50) | 1] | add // 0)}' 

使用给定的输入（已进行更正） ，输出为：

With the given input (after corrections have been made), the output would be:


{
testId： 1，
numStudents ：1
}
{
testId： 2，
numStudents：2
}
{
testId ： 3，
numStudents：0
}


使用 length ，例如

{testId,
 numStudents: ([select(.studentId[].score > 50) ] | length)}

但是，如果您不介意添加'def'，则最好的解决方案（例如，因为它不涉及中间数组的构造）将遵循以下几行：

However, if you don't mind adding a 'def', then the best solution (e.g. because it does not involve construction of an intermediate array) would be along the following lines:

def count(s): reduce s as $i (0; .+1);

{testId, numStudents: count(select(.studentId[].score > 50))} 

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