你已經把NumPy的標籤上的問題,所以我」假設你需要NumPy語法,這是我之前的答案不使用的。
如果實際上你想使用NumPy,那麼你可能不希望數組中的字符串,否則你將不得不將浮點數表示爲字符串。
你在找什麼是的NumPy的語法按行訪問一個二維數組的元素(並排除第一列)。
即語法是:噸第二場景
M[row_index,1:] # selects all but 1st col from row given by 'row_index'
W/R /在Question-- 選擇非相鄰列:
M[row_index,[0,2]] # selects 1st & 3rd cols from row given by 'row_index'
小併發症你的問題只是你想爲row_index使用一個字符串,所以有必要刪除字符串(這樣你可以創建一個2D NumPy數組的浮點數),用數字代替它們行索引,然後創建一個查表的字符串和數值行索引地圖:
>>> 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])
第二種情況在你的問題:如果索引列的變化?
>>> # 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])
什麼是「foo」,「bar」等?字符串?或者只是其他數字的佔位符? –
你怎麼能構建一個包含*既*浮動和字符串的numpy數組? – talonmies
@tal從數據庫。 – Merlin