你已经把NumPy的标签上的问题,所以我”假设你需要NumPy语法,这是我之前的答案不使用的。
如果实际上你想使用NumPy,那么你可能不希望数组中的字符串,否则你将不得不将浮点数表示为字符串。
你在找什么是的NumPy的语法按行访问一个二维数组的元素(并排除第一列)。
即语法是:吨第二场景
M[row_index,1:] # selects all but 1st col from row given by 'row_index'
W/R /在Question-- 选择非相邻列:
M[row_index,[0,2]] # selects 1st & 3rd cols from row given by 'row_index'
小并发症你的问题只是你想为row_index使用一个字符串,所以有必要删除字符串(这样你可以创建一个2D NumPy数组的浮点数),用数字代替它们行索引,然后创建一个查表的字符串和数值行索引地图:
>>> import numpy as NP
>>> # create a look-up table so you can remove the strings from your python nested list,
>>> # which will allow you to represent your data as a 2D NumPy array with dtype=float
>>> keys
['foo', 'bar', 'noo', 'tar', 'boo']
>>> values # 1D index array comprised of one float value for each unique string in 'keys'
array([0., 1., 2., 3., 4.])
>>> LuT = dict(zip(keys, values))
>>> # add an index to data by inserting 'values' array as first column of the data matrix
>>> A = NP.hstack((vals, A))
>>> A
NP.array([ [ 0., .567, .611],
[ 1., .469, .479],
[ 2., .22, .269],
[ 3., .48, .508],
[ 4., .324, .324] ])
>>> # so now to look up an item, by 'key':
>>> # write a small function to perform the look-ups:
>>> def select_row(key):
return A[LuT[key],1:]
>>> select_row('foo')
array([ 0.567, 0.611])
>>> select_row('noo')
array([ 0.22 , 0.269])
第二种情况在你的问题:如果索引列的变化?
>>> # e.g., move index to column 1 (as in your Q)
>>> A = NP.roll(A, 1, axis=1)
>>> A
array([[ 0.611, 1. , 0.567],
[ 0.479, 2. , 0.469],
[ 0.269, 3. , 0.22 ],
[ 0.508, 4. , 0.48 ],
[ 0.324, 5. , 0.324]])
>>> # the original function is changed slightly, to select non-adjacent columns:
>>> def select_row2(key):
return A[LuT[key],[0,2]]
>>> select_row2('foo')
array([ 0.611, 0.567])
什么是“foo”,“bar”等?字符串?或者只是其他数字的占位符? –
你怎么能构建一个包含*既*浮动和字符串的numpy数组? – talonmies
@tal从数据库。 – Merlin