Вы можете сделать это, используя reduce
.
const records = {
138: {date: "2020-02-18", state: "California", fips: "06", cases: "7", deaths: "2"},
139: {date: "2020-02-18", state: "Illinois", fips: "17", cases: "2", deaths: "0"},
140: {date: "2020-02-18", state: "Massachusetts", fips: "25", cases: "1", deaths: "0"},
141: {date: "2020-02-18", state: "Nebraska", fips: "31", cases: "10", deaths: "0"},
142: {date: "2020-02-18", state: "Texas", fips: "48", cases: "2", deaths: "0"},
143: {date: "2020-02-18", state: "Washington", fips: "53", cases: "1", deaths: "2"},
144: {date: "2020-02-18", state: "Wisconsin", fips: "55", cases: "1", deaths: "0"},
145: {date: "2020-02-19", state: "Arizona", fips: "04", cases: "1", deaths: "0"},
146: {date: "2020-02-19", state: "California", fips: "06", cases: "7", deaths: "0"},
147: {date: "2020-02-19", state: "Illinois", fips: "17", cases: "2", deaths: "0"},
148: {date: "2020-02-19", state: "Massachusetts", fips: "25", cases: "1", deaths: "0"},
149: {date: "2020-02-19", state: "Nebraska", fips: "31", cases: "10", deaths: "0"},
150: {date: "2020-02-19", state: "Texas", fips: "48", cases: "2", deaths: "0"},
151: {date: "2020-02-19", state: "Washington", fips: "53", cases: "1", deaths: "0"},
152: {date: "2020-02-19", state: "Wisconsin", fips: "55", cases: "1", deaths: "0"},
153: {date: "2020-02-20", state: "Arizona", fips: "04", cases: "1", deaths: "0"},
154: {date: "2020-02-20", state: "California", fips: "06", cases: "8", deaths: "0"},
155: {date: "2020-02-20", state: "Illinois", fips: "17", cases: "2", deaths: "0"},
156: {date: "2020-02-20", state: "Massachusetts", fips: "25", cases: "1", deaths: "0"},
157: {date: "2020-02-20", state: "Nebraska", fips: "31", cases: "11", deaths: "0"}
};
const res = Object.values(records).reduce((acc, {date, cases, deaths}) => {
if (acc[date] !== undefined) {
acc[date].totalCases += (+cases);
acc[date].totalDeaths += (+deaths);
} else {
acc[date] = {date, totalCases: (+cases), totalDeaths: (+deaths)};
}
return acc;
}, {});
console.log(res);
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