我需要对水文地质野外工作的大型数据集进行一些分析。我正在使用NumPy。我想知道如何:
例如我的数组的第二列,以数字表示(例如5.2)。然后
计算该列中数字的累加和。
正如我提到的,我只想处理特定的列,而不要处理整个数组。
you can do this in two simple steps using NumPy:
>>> # multiply column 2 of the 2D array, A, by 5.2
>>> A[:,1] *= 5.2
>>> # assuming by 'cumulative sum' you meant the 'reduced' sum:
>>> A[:,1].sum()
>>> # if in fact you want the cumulative sum (ie, returns a new column)
>>> # then do this for the second step instead:
>>> NP.cumsum(A[:,1])
带有一些模拟数据:
>>> A = NP.random.rand(8, 5)
>>> A
array([[ 0.893, 0.824, 0.438, 0.284, 0.892],
[ 0.534, 0.11 , 0.409, 0.555, 0.96 ],
[ 0.671, 0.817, 0.636, 0.522, 0.867],
[ 0.752, 0.688, 0.142, 0.793, 0.716],
[ 0.276, 0.818, 0.904, 0.767, 0.443],
[ 0.57 , 0.159, 0.144, 0.439, 0.747],
[ 0.705, 0.793, 0.575, 0.507, 0.956],
[ 0.322, 0.713, 0.963, 0.037, 0.509]])
>>> A[:,1] *= 5.2
>>> A
array([[ 0.893, 4.287, 0.438, 0.284, 0.892],
[ 0.534, 0.571, 0.409, 0.555, 0.96 ],
[ 0.671, 4.25 , 0.636, 0.522, 0.867],
[ 0.752, 3.576, 0.142, 0.793, 0.716],
[ 0.276, 4.255, 0.904, 0.767, 0.443],
[ 0.57 , 0.827, 0.144, 0.439, 0.747],
[ 0.705, 4.122, 0.575, 0.507, 0.956],
[ 0.322, 3.71 , 0.963, 0.037, 0.509]])
>>> A[:,1].sum()
25.596156138451427
仅需要一些简单的规则即可在NumPy中进行元素选择(索引):
NumPy,就像Python,也是基于0的,因此例如下面的“ 1”是指第二列
逗号将括号内的尺寸分开,因此[行,列],例如A [2,3]表示第三行第四列的项目(“单元格”)>]
冒号表示该维度上元素的all
确定:
将常数与特定的列或行相乘: