Question

我构建了一个从数据库中请求图像URL的webservis。而我想在迅速展示它。但是我在var photo line上发现了这个错误：

无法将'subSequence'类型的值（又名'String.CharacterView'）转换为集合中的'String'类型

let requestResponse = self.sendToServer(postUrl: "localhost",data:"abc")

let Seperated = requestResponse.characters.split(separator: " ")

var photo = Seperated[0] as String

let imageURL = URL(string: photo)
if let imageData = try? Data(contentsOf: imageURL!) {
    ...
}

Answer 1

考虑这样的事情：

let requestResponse = "some string"
let separated = requestResponse.characters.split(separator: " ")

if let some = separated.first {
    let value = String(some)

    // Output: "some"
}

Answer 2

如果使用Swift 4，您将像这样使用

：

let separated = requestResponse.split(separator: " ")
var photo = String(separated.first ?? "")

Answer 3

split返回Substring的列表，因此我们必须将它们映射（转换）为String。为此，您只需将Substring传递给String的{{1}}函数：

init

Answer 4

一种通过使用高阶函数分割字符串来获取字符串的方法：

best_results = {}
seeds = [1, 3, 5, 7, 11, 13, 17, 19]

#find best hyperparameters c and gamma
for seed in seeds:
    result = {'best_c' : 0.0, 'best_gamma' : 0.0, 'best_score' : 0.0 } 
    X_train, X_test, Y_train, Y_test = train_test_split(X, y, test_size=0.1, random_state=seed)

    for C in np.linspace(10.0, 200, 40):
        for gamma in np.linspace(0.001, 0.01, 20):
            rbf_clf = svm.SVC(C = C, gamma = gamma)
            scores = cross_val_score(rbf_clf, X_train, Y_train, cv=10, n_jobs=-1)
            if(scores.mean() > result['best_score']):
                  result = {'best_c' : C, 'best_gamma' : gamma, 'best_score' : scores.mean() } 

    index = "%0.3f%0.3f"%(result['best_c'], result['best_gamma'])
    if(not index in best_results):
        best_results[index] = []
    best_results[index].append(result)


best_index = ""
moda = 0
for index in best_results:
    if(len(best_results[index]) > moda):
        moda = len(best_results[index])
        best_index = index

# get the accuracy of my model
best_c = best_results[best_index][0]['best_c']
best_gamma = best_results[best_index][0]['best_gamma']
test_scores = np.zeros(len(seeds))
for i in range(0,len(seeds)):
    seed = seeds[i]
    X_train, X_test, Y_train, Y_test = train_test_split(X, y, test_size=0.1, random_state=seed)
    rbf_clf = svm.SVC(C = best_c, gamma = best_gamma)
    rbf_clf.fit(X_train, Y_train)
    test_scores[i] = rbf_clf.score(X_test, Y_test)

print("C:%0.3f\t Gamma:%0.5f\t Accuracy:%0.5f" %(best_c, best_gamma, test_scores.mean()))

Answer 5

最简单的解决方案。

let Seperated = requestResponse.characters.split(separator: " ").map { String($0) }

无法将'subSequence'类型的值（也称为'String.CharacterView'）转换为在集合中键入'String'

5 个答案: