## Numpy如何对数字和数组求和？内容来源于 Stack Overflow，并遵循CC BY-SA 3.0许可协议进行翻译与使用

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### 2 个回答

```import numpy as np
data = np.arange(1, 7)
groups = np.array([0,0,1,2,2,1])

unique_groups = np.unique(groups)
sums = []
for group in unique_groups:
sums.append(data[groups == group].sum())```

```import numpy as np
data = np.arange(1, 7)
groups = np.array([0,0,1,2,2,1])

unique_groups = np.unique(groups)

# Forgive the bad naming here...
# I can't think of more descriptive variable names at the moment...
x, y = np.meshgrid(groups, unique_groups)
data_stack = np.tile(data, (unique_groups.size, 1))

data_in_group = np.zeros_like(data_stack)
data_in_group[x==y] = data_stack[x==y]

sums = data_in_group.sum(axis=1)```

```def sum_by_group(values, groups):
order = np.argsort(groups)
groups = groups[order]
values = values[order]
values.cumsum(out=values)
index = np.ones(len(groups), 'bool')
index[:-1] = groups[1:] != groups[:-1]
values = values[index]
groups = groups[index]
values[1:] = values[1:] - values[:-1]
return values, groups```