ValueError: Expected 2D array, got 1D array instead:

本文记录了使用Apache Spark进行支持向量机(SVM)训练过程中遇到的问题及解决方案。主要问题为预测阶段出现的一维数组错误,并给出了正确的特征reshape方法。
18/08/19 22:01:52 WARN NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Parsing data
Fitting model
train
Currently 8 partitions left
Size of data: 60000
Currently 4 partitions left
Size of data: 28024
Currently 2 partitions left
Warning: 456.0 relevant support vectors thrown away!
('model.support:', array([   0,    1,    3, ..., 7018, 7020, 7021], dtype=int32), ' self.max_sv:', 5000.0)
Warning: 484.0 relevant support vectors thrown away!
('model.support:', array([   0,    1,    3, ..., 7065, 7066, 7067], dtype=int32), ' self.max_sv:', 5000.0)
Warning: 348.0 relevant support vectors thrown away!
('model.support:', array([   0,    1,    2, ..., 6891, 6892, 6893], dtype=int32), ' self.max_sv:', 5000.0)
Warning: 453.0 relevant support vectors thrown away!
('model.support:', array([   1,    2,    4, ..., 7036, 7038, 7039], dtype=int32), ' self.max_sv:', 5000.0)
Size of data: 20000
Warning: 2935.0 relevant support vectors thrown away!
('model.support:', array([   9,   19,   23, ..., 9975, 9976, 9984], dtype=int32), ' self.max_sv:', 5000.0)
Warning: 2923.0 relevant support vectors thrown away!
('model.support:', array([  13,   35,   42, ..., 9968, 9970, 9996], dtype=int32), ' self.max_sv:', 5000.0)
Time: 845.46
Predicting outcomes training set
18/08/19 22:16:16 ERROR Executor: Exception in task 1.0 in stage 9.0 (TID 19)
org.apache.spark.api.python.PythonException: Traceback (most recent call last):
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/worker.py", line 229, in main
    process()
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/worker.py", line 224, in process
    serializer.dump_stream(func(split_index, iterator), outfile)
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/rdd.py", line 2438, in pipeline_func
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/rdd.py", line 2438, in pipeline_func
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/rdd.py", line 2438, in pipeline_func
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/rdd.py", line 362, in func
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/rdd.py", line 1056, in <lambda>
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/rdd.py", line 1056, in <genexpr>
  File "/home/hduser/pythonwork/CVM/bin/mnist.py", line 57, in <lambda>
    labelsAndPredsTrain = trainRDD.map(lambda p: (p.label, model.predict(p.features)))
  File "/home/hduser/pythonwork/CVM/cvm/svm.py", line 20, in predict
    return self.model.predict(features)
  File "/home/hduser/anaconda2/lib/python2.7/site-packages/sklearn/svm/base.py", line 548, in predict
    y = super(BaseSVC, self).predict(X)
  File "/home/hduser/anaconda2/lib/python2.7/site-packages/sklearn/svm/base.py", line 308, in predict
    X = self._validate_for_predict(X)
  File "/home/hduser/anaconda2/lib/python2.7/site-packages/sklearn/svm/base.py", line 439, in _validate_for_predict
    X = check_array(X, accept_sparse='csr', dtype=np.float64, order="C")
  File "/home/hduser/anaconda2/lib/python2.7/site-packages/sklearn/utils/validation.py", line 441, in check_array
    "if it contains a single sample.".format(array))
ValueError: Expected 2D array, got 1D array instead:
array=[0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.08627451 0.         0.         0.01960784
 0.2745098  0.2745098  0.2745098  0.2745098  0.2745098  0.2745098
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.00784314 0.30980392 0.91372549
 0.98039216 0.96862745 0.96862745 0.96862745 0.99607843 0.98039216
 0.93333333 0.93333333 0.84313725 0.47843137 0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.02352941 0.22745098
 0.41176471 0.61176471 0.99607843 0.99607843 0.9372549  0.78823529
 0.45098039 0.54117647 0.49803922 0.18431373 0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.03529412 0.61176471 0.99607843 0.51764706 0.14901961
 0.55294118 0.56862745 0.09411765 0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.63921569
 0.9254902  0.24313725 0.00392157 0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.11764706 0.98039216 0.33333333 0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.19215686 0.98823529 0.58431373 0.09803922 0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.02745098 0.23529412
 0.99607843 0.94509804 0.80392157 0.34901961 0.         0.
 0.         0.         0.         0.01960784 0.44313725 0.18431373
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.04705882 0.49411765
 0.98039216 1.         0.75686275 0.02745098 0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.05098039 0.31372549 0.8627451
 0.94901961 0.45882353 0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.1254902  0.8        0.96078431
 0.35294118 0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.03529412 0.30980392 0.00784314 0.         0.         0.
 0.         0.         0.02352941 0.89019608 0.81176471 0.01568627
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.32156863 0.6745098
 0.03137255 0.         0.         0.         0.         0.
 0.23529412 0.78039216 0.74509804 0.05098039 0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.54117647 0.96862745 0.58039216 0.5254902
 0.24313725 0.24313725 0.24313725 0.50196078 0.92156863 0.84705882
 0.41176471 0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.18039216 0.6        0.74509804 0.78039216 0.96470588 0.96470588
 0.96470588 0.92941176 0.6627451  0.16862745 0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.         0.         0.
 0.         0.         0.         0.        ].
Reshape your data either using array.reshape(-1, 1) if your data has a single feature or array.reshape(1, -1) if it contains a single sample.

    at org.apache.spark.api.python.BasePythonRunner$ReaderIterator.handlePythonException(PythonRunner.scala:298)
    at org.apache.spark.api.python.PythonRunner$$anon$1.read(PythonRunner.scala:438)
	at org.apache.spark.api.python.PythonRunner$$anon$1.read(PythonRunner.scala:421)
    at org.apache.spark.api.python.BasePythonRunner$ReaderIterator.hasNext(PythonRunner.scala:252)
    at org.apache.spark.InterruptibleIterator.hasNext(InterruptibleIterator.scala:37)
    at scala.collection.Iterator$class.foreach(Iterator.scala:893)
    at org.apache.spark.InterruptibleIterator.foreach(InterruptibleIterator.scala:28)
    at scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:59)
    at scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:104)
    at scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:48)
    at scala.collection.TraversableOnce$class.to(TraversableOnce.scala:310)
    at org.apache.spark.InterruptibleIterator.to(InterruptibleIterator.scala:28)
    at scala.collection.TraversableOnce$class.toBuffer(TraversableOnce.scala:302)
    at org.apache.spark.InterruptibleIterator.toBuffer(InterruptibleIterator.scala:28)
    at scala.collection.TraversableOnce$class.toArray(TraversableOnce.scala:289)
    at org.apache.spark.InterruptibleIterator.toArray(InterruptibleIterator.scala:28)
    at org.apache.spark.rdd.RDD$$anonfun$collect$1$$anonfun$12.apply(RDD.scala:939)
    at org.apache.spark.rdd.RDD$$anonfun$collect$1$$anonfun$12.apply(RDD.scala:939)
    at org.apache.spark.SparkContext$$anonfun$runJob$5.apply(SparkContext.scala:2067)
	at org.apache.spark.SparkContext$$anonfun$runJob$5.apply(SparkContext.scala:2067)
    at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:87)
    at org.apache.spark.scheduler.Task.run(Task.scala:109)
    at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:345)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

解决方法:

    labelsAndPredsTrain = trainRDD.map(lambda p: (p.label, model.predict(p.features.reshape(1,-1))))

在feature后增加reshape方法.
说明:

>>> a = [1,2,3,4]
>>> import numpy as np
>>> b = np.array(a)
>>> c = b.reshape(1,-1)
>>> print c
[[1 2 3 4]]
>>> print b
[1 2 3 4]
>>> print a
[1, 2, 3, 4]
<think>好的,用户遇到了ValueError,提示“Expected 2D array, got 1D array instead”,这通常在使用某些机器学习库(比如scikit-learn)时出现,因为它们要求输入是二维数组。用户需要知道如何将一维数组转换为二维数组来解决这个问题。 首先,我应该回顾一下NumPy的reshape方法。用户可能对reshape的参数不太熟悉,特别是-1的用法。需要解释清楚reshape(-1,1)和reshape(1,-1)的区别,以及何时使用哪种方式。例如,当数据是单一特征时,使用reshape(-1,1)来变成二维数组,每行一个样本;如果是单一样本,则用reshape(1,-1)。 然后,需要引用用户提供的例子,比如引用[1]和引用[2]中的内容,说明reshape的具体应用场景。比如StandardScaler在scikit-learn中需要二维输入,这时候必须转换。 还要考虑用户可能的代码示例,给出具体的Python代码片段,比如使用numpy的reshape函数或者直接修改数组结构。比如用户可能有一个一维数组array,通过array.reshape(-1,1)转换成二维。 另外,需要提醒用户注意转换后的形状是否符合库函数的要求。例如,某些模型需要(n_samples, n_features),所以正确的转换方式很重要。如果用户误用了reshape(1,-1),可能会导致样本数错误,应该指出这点。 可能还需要提到flatten或ravel方法,但这里的问题是从一维转二维,所以重点在reshape。同时,可以说明在机器学习中的常见情况,比如特征标准化时的处理。 最后,总结解决步骤:确定数据是单一特征还是单一样本,选择合适的reshape方法,应用在数据预处理步骤中,并验证形状是否正确。确保用户理解为什么会出现这个错误,以及如何根据具体情况调整数组维度。</think>在Python中遇到`ValueError: Expected 2D array, got 1D array instead`错误时,通常是因为某些机器学习库(如scikit-learn)要求输入数据为二维数组,但实际传入的是一维数组。以下是详细解决方法: --- ### 1. **理解错误原因** 大多数机器学习模型的输入需要二维数组格式,例如: - 二维数组形状为`(n_samples, n_features)`,表示`n_samples`个样本,每个样本包含`n_features`个特征。 - 若输入一维数组(形状为`(n,)`),则会触发维度不匹配的错误。 --- ### 2. **使用`reshape`方法转换维度** 通过NumPy或Pandas的`reshape`方法调整数组形状: - **情况1:数据为单一特征** 若数据是单个特征(如`[1, 2, 3, 4]`),需转换为`(n_samples, 1)`,即每行一个样本: ```python import numpy as np array_1d = np.array([1, 2, 3, 4]) array_2d = array_1d.reshape(-1, 1) # 形状变为(4, 1) ``` - **情况2:数据为单个样本** 若数据是单个样本的多个特征(如`[0.1, 0.2, 0.3]`),需转换为`(1, n_features)`: ```python array_2d = array_1d.reshape(1, -1) # 形状变为(1, 3) ``` --- ### 3. **在预处理流程中应用** 以`StandardScaler`为例,标准化前需确保数据为二维: ```python from sklearn.preprocessing import StandardScaler # 原始一维数据 raw_data = np.array([1, 2, 3, 4, 5]) # 转换为二维后再标准化 scaled_data = StandardScaler().fit_transform(raw_data.reshape(-1, 1)) # 若需恢复为一维(可选) scaled_data_1d = scaled_data.reshape(-1) ``` 引用示例中提到,通过`reshape(-1,1)`将数据转换为二维,标准化后再用`reshape(-1)`转回一维(若需要)[^2]。 --- ### 4. **验证形状** 转换后可通过`shape`属性检查维度: ```python print(array_2d.shape) # 应输出类似(n_samples, n_features) ``` --- ### 常见场景示例 | 原始数据形状 | 目标形状 | 转换方法 | 适用场景 | |--------------|-------------------|--------------------|------------------------| | `(n,)` | `(n, 1)` | `reshape(-1, 1)` | 单特征多样本(如回归) | | `(n,)` | `(1, n)` | `reshape(1, -1)` | 多特征单样本(如预测) | --- ### 5. **其他方法** - **使用`np.newaxis`扩展维度** ```python array_2d = array_1d[:, np.newaxis] # 等效于reshape(-1, 1) ``` - **Pandas DataFrame转换** 若数据为Series,可转换为DataFrame: ```python import pandas as pd df = pd.DataFrame({'feature': array_1d}) ``` --- 通过上述方法,可有效避免维度不匹配错误。关键是根据数据含义选择`reshape(-1,1)`(单特征)或`reshape(1,-1)`(单样本)[^1]。 ---
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