java - 如何从java中的ArrayList中删除重复条目

Question

我想删除基于 productId 和 priceTagId 的重复条目。如果我们删除重复项，我们需要添加数量

在 productDetails 列表中有相同的 productId 但数量不同，如果我需要将数量加到一个中

"productDetails" : [
        {
            "productId" : "5764dfb7d991390e25edff74",
            "quantity" : 2,
            "netQty" : "10mg",
            "priceTagId" : 1,
            "alertAvailablity" : "Success"
        },
        {
            "productId" : "5764dfb7d991390e25edff74",
            "quantity" : 4,
            "netQty" : "10mg",
            "priceTagId" : 1,
            "alertAvailablity" : "Success"
        },
        {
            "productId" : "5764dfb7d991390e25edff74",
            "quantity" : 6,
            "netQty" : "30mg",
            "priceTagId" : 3,
            "alertAvailablity" : "Success"
        },
        {
            "productId" : "5764dfb7d991390e25edff74",
            "quantity" : 8,
            "netQty" : "30mg",
            "priceTagId" : 3,
            "alertAvailablity" : "Success"
        },
        {
            "productId" : "2345dfb7d991390e25edf659",
            "quantity" : 8,
            "netQty" : "30mg",
            "priceTagId" : 3,
            "alertAvailablity" : "Success"
        }
    ],

我得到的最终输出为

"productDetails" : [
        {
            "productId" : "5764dfb7d991390e25edff74",
            "quantity" : 6,
            "netQty" : "10mg",
            "priceTagId" : 1,
            "alertAvailablity" : "Success"
        },
        {
            "productId" : "5764dfb7d991390e25edff74",
            "quantity" : 14,
            "netQty" : "30mg",
            "priceTagId" : 3,
            "alertAvailablity" : "Success"
        },
        {
            "productId" : "2345dfb7d991390e25edf659",
            "quantity" : 8,
            "netQty" : "30mg",
            "priceTagId" : 3,
            "alertAvailablity" : "Success"
        }

    ],

根据 productId 和 priceTagId，我需要删除重复项并从删除的重复项中添加数量

private List<ProductDetail> removeDuplicateProducts(List<ProductDetail> productDetails) throws BaseException {
    for (ProductDetail eachProductDetail : productDetails) {
        for (ProductDetail eachInnerProductDetail : productDetails) {
            if(eachProductDetail.getProductId().equals(eachInnerProductDetail.getProductId()))
            {
                if(eachProductDetail.getPriceTagId().equals(eachInnerProductDetail.getPriceTagId()))
                {
                    eachProductDetail.setQuantity(eachProductDetail.getQuantity()+eachInnerProductDetail.getQuantity());
                    productDetails.clear();
                }
            }

        }
    }           
    return productDetails;
}

但我不明白吗？怎么了？

Answer 1

最有效的解决方案是使用 Map，其中键是您认为使产品相同的所有字段的组合，值包含任何附加信息。

在你的情况下你可以做

private Collection<ProductDetail> accumulateDuplicateProducts(List<ProductDetail> productDetails) {
    // use a map to quickly find entries which match.
    // using a linked HashMap means the order of addition is preserved.
    Map<String, ProductDetail> productMap = new LinkedHashMap<>();
    for (ProductDetail pd : productDetails) {
        // build a composite key of the fields you want to match on.
        String key = pd.getProductId() + " " + pd.getPriceTag();
        // if the Strings match they should be merged.
        // if there was no previous entry, use the current one.
        // if there was a previous entry call merge() to combine them.
        productMap.compute(key, (k, pd2) -> pd2 == null ? pd : merge(pd, pd2));
    }
    return productMap.values();
}

private static ProductDetail merge(ProductDetail pd, ProductDetail pd2) {
    // combine two ProductDetails
}

注意:如果使用两个嵌套循环，时间复杂度是 O(n) 而不是 O(n^2)。

But i dint get it wy? What wrong?

你遇到的一个问题是

productDetails.clear();

您遇到的另一个问题是您将每个条目与每个条目进行比较，例如假设您有两个条目 A 和 B 匹配

A is compared with A so A *= 2
A is compared with B do A += B
B is compared with A so B += A
B is compared with B so B *= 2

您最终还是得到了两个条目，因为您没有删除一个条目。