Python 如何在for循环中追加pandas.DataFrame中的行

嗨，我正在尝试在新创建的数据框中追加行

###expression
for i in active_brain_regions:
    indices = np.where(LM == i)
    expr = gene[indices]
    mean = np.mean(expr)
    dat= [[i, mean, str("nifti")]]
    dd = pd.DataFrame(dat, columns = ['region', 'mean expr', 'gene_id'])
    dd.append(dd)

dd应该看起来像

 0.0  -0.424069   nifti
 1.0       -1.0   nifti
 .
 . 
 .
 11.0    0.23352   nifti

---

但是在运行for循环之后，dd只是一个大小为（1,3）的数据帧，最后一个条目是区域11。

您可以分配回，因为使用了以下方法：

或者使用纯python

append

（就地工作）创建数据帧列表，并仅使用一次：

L = []
for i in active_brain_regions:
    indices = np.where(LM == i)
    expr = gene[indices]
    mean = np.mean(expr)
    dat= [[i, mean, str("nifti")]]
    dd = pd.DataFrame(dat, columns = ['region', 'mean expr', 'gene_id'])
    L.append(dd)

 df = pd.concat(L, ignore_index=True)

L = []
for i in active_brain_regions:
    indices = np.where(LM == i)
    expr = gene[indices]
    mean = np.mean(expr)
    dat= [[i, mean, str("nifti")]]
    L.append(dat)

 df = pd.DataFrame(L, columns = ['region', 'mean expr', 'gene_id'])

但最快的解决方案应该是创建列表列表并只向

DataFrame

构造函数传递一次：

L = []
for i in active_brain_regions:
    indices = np.where(LM == i)
    expr = gene[indices]
    mean = np.mean(expr)
    dat= [[i, mean, str("nifti")]]
    dd = pd.DataFrame(dat, columns = ['region', 'mean expr', 'gene_id'])
    L.append(dd)

 df = pd.concat(L, ignore_index=True)

L = []
for i in active_brain_regions:
    indices = np.where(LM == i)
    expr = gene[indices]
    mean = np.mean(expr)
    dat= [[i, mean, str("nifti")]]
    L.append(dat)

 df = pd.DataFrame(L, columns = ['region', 'mean expr', 'gene_id'])