对 csv 中的值进行计算

Question

我有一个 csv 文件，格式为

100000000,0.0565325,-122.797,0.9984,-32.5345,0.9984,-32.5345,0.0565325,-122.271
101000000,0.0570362,-123.125,0.998372,-32.8592,0.998372,-32.8592,0.0570362,-122.593
102000000,0.0575381,-123.452,0.998343,-33.1838,0.998343,-33.1838,0.0575381,-122.915
103000000,0.0580382,-123.779,0.998314,-33.5085,0.998314,-33.5085,0.0580382,-123.237

并使用 绘制数据pgfplots。但是我想“操纵”这些值

• 将第一列除以 $10^9$ (Hz->GHz)
• 执行“20log(abs(x))”，因为 x 以线性形式给出并且需要以 dB 为单位绘制。

我在 pgfplots 文档中发现了 4 次出现，calc但这些案例并不处理读取信息。

我知道情节不匹配。

Answer 1

欢迎使用 TeX.SX！您可以使用选项x expr和y expr对从表中读取的数据（来自文件或内联）执行计算。

如果您的数据没有列名，您可以使用\thisrowno来访问相关列中的数据（\thisrowno{0}描述第一列）。如果列有名称，您可以使用 来访问相关数据中的数据\thisrow{<column name>}。

因此，例如，您可以写入y expr={20*log10(abs(\thisrowno{1}))}对 CSV 数据第二列的值应用 20 log(abs(x))。

我不确定以下内容是否是您想要的，因为您没有提供最小工作示例（MWE），但它至少可以让你入门：

\documentclass[border=10mm]{standalone}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.18}

\begin{filecontents}{data.csv}
100000000,0.0565325,-122.797,0.9984,-32.5345,0.9984,-32.5345,0.0565325,-122.271
101000000,0.0570362,-123.125,0.998372,-32.8592,0.998372,-32.8592,0.0570362,-122.593
102000000,0.0575381,-123.452,0.998343,-33.1838,0.998343,-33.1838,0.0575381,-122.915
103000000,0.0580382,-123.779,0.998314,-33.5085,0.998314,-33.5085,0.0580382,-123.237
\end{filecontents}

\pgfplotstableread[col sep=comma, header=false]{data.csv}\datatable

\begin{document}

\begin{tikzpicture}
    \begin{axis}[
            xlabel={GHz}, 
            ylabel={dB},
            xtick=data, 
            x tick label style={
                /pgf/number format/precision=3,
                /pgf/number format/fixed,
                /pgf/number format/fixed zerofill
            }
        ]  
        \addplot table[
            x expr={\thisrowno{0}/1e9}, 
            y expr={20*log10(abs(\thisrowno{1}))}
        ] {\datatable};
    \end{axis} 
\end{tikzpicture}

\end{document}