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IntroductionThis document contains R code that can be used to transform two-mode service value matrices (svm) into one-mode inter-city connectivity matrices (icc) using the interlocking network model (inm) , and subsequently compute the global network connectivity (gnc) for every city. Details on the input matrices, the model, and its output can be found in . is a free software environment that provides a wide variety of statistical techniques. R needs to be downloaded, together with a development environment that supports direct code execution, and tools for plotting, history, debugging and workspace management. We used Rstudio and generated this document with R Markdown. R Markdown is designed for easier reproducibility, because both computing code and narratives are in the same document. The code runs with the “dplyr”-package. The below example refers to the 2018 data as shown by the file names, but the code works with any other service value matrix in .csv-format as long as it is properly structured. Basically, three steps are explained in this brief guide: (i) creating a numerical service value matrix; (ii) computing the inter-city connectivity matrix and (iii) generating a table with global network connectivities. Step 1 - Creating a numerical service value matrixFirst of all, GaWC’s two-mode service value matrix needs to be read and stored. Data are stored in a dataframe called ‘svm’ with the following code:
A dataframe can contain characters, strings and numbers, and is therefore not fit for matrix algebra. We extract the cities and firms from the dataframe and transform what is left into a numerical matrix ‘svm_mat’ (dimensions: 175 firms x 707 cities) as follows:
Step 2 - Constructing inter-city connectivity matrixThe icc matrix is basically the product of the svm matrix and its transpose (Derudder, 2020). This can easily be done with the tcrossprod-function. Keep in mind that the diagonals are zero.
Step 3 - Calculating global network connectivity for every cityTo calculate absolute and relative global network connectivity for every city, we use code that calculates the total icc-value for every city (which is the absolute GNC-value), and sorts the output. We add a GNC_rel value and a rank to the table.
* Tom Storme and Ben Derudder, SEG Research Group, Ghent University, 1 April 2020 |
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